In Unsong chapter "Interlude ד: N-Grammata" (9 March 2016), the protagonist Aaron concludes off the Name of God and the shortest version of it, 'H', that:

...And “he” corresponds to the English letter H. H is for hydrogen, the very beginning of the periodic table, the building block out of which everything else is made. H is the fundamental unit of matter in the universe. H, the saying goes, is a colorless odorless gas which, given enough time, tends to turn into people. How would that make sense unless H was God, the organizing and ordering principle of the Cosmos, He who creates all things? And then there was my crazy great-uncle. Invented a bomb that could destroy the world, the deadliest and most terrifying object any human being has ever produced – and slapped an H in front of the name. I still wonder, every so often, if he was a hidden kabbalist. It takes a certain amount of obsessiveness to be as reckless as he was. That’s how I picture him, actually, studying Torah by night, figuring out new ways to annihilate cities by day. What sort of religion must such a man have? What kind of relationship with God? What soteriology? What theodicy? All I have to guide me is that one old book, the only thing my father gave me:

H has become a most troublesome letter
It means something bigger, if not something better.

What are we to say to that?

But what are the rest of Edward Teller's rhymes?

---

There is no clear source or canonical version, so I began searching. In chronological order:

1. Transformations: Thinking Through Feminism, ed Ahmed 2000, pg240, Carol Wolkowitz paper states:

   This 'birth of the bomb' discourse was incorporated by women into their own life stories. For instance, Joanne Gailar's chapter on early Oak Ridge, written in 1947 while pregnant with her first child, is called "A Man, A Woman, A-Bomb" and Charlotte Serber's account of women's paid employment is called "Labour Pains" (in Wilson and Serber 1988). Laura Fermi's [1954] autobiography, Atoms in the Family: My Life With Enrico Fermi, presents the inventors of the bomb as family men. Children, she says, became aware that their "ordinary fathers", who "scolded and explained how to use a chemistry set ... who took too long shaving in the bathroom, who wore white badges on their coats, who ate their meals and went off to work ... those men were important people" (1954:258-259).

   These images of domesticated masculinity are not about patriarchal authority but about fathers reduced to squabbling with their children. [Laura] Fermi goes on to domesticate atomic bombs and their inventors still further, quoting from the alphabet Edward Teller concocted for his son Paul:

    A stands for atom; it is so small
    No one has ever seen it at all.
   
    B stands for bomb; the bombs are much bigger,
    So brother, do not be too fast on the trigger.
   
    S stands for secret; you can keep it forever
    Provided there's no one abroad who is clever
        (1954:238)
   

2. Laura Fermi's original 1954 passage with context, pg221-222:

   He did not escape the fate of most physicists who were doomed to move over the country until the end of the war. He left Washington in 1940 to spend a year at Columbia University. From there he did not go back to Washington but moved on to Chicago, to California, and back to Chicago, according to the needs of the uranium project.

   He was among the first to follow Oppie to Los Alamos. There I found him with his wife, his year-old son Paul, and the monumental grand piano that had followed him through his peregrinations. Like many theoreticians, Edward was extremely fond of music, and he devoted to it a good portion of his spare time...Edward had become a prominent figure on the mesa by the time I arrived there...When he could forget his worries Edward delighted in simple pleasures. His favorite author was Lewis Carroll, and he started to read Carroll's stories and poems to his son Paul long before the child could understand them. Edward could be as playful and as naive as his little boy, and each day the two of them spent some time entertaining each other. Edward started an alphabet for Paul, of which the following lines are an except:

    𝘈 stands for atom; it is so small  
    No one has ever seen it at all.
   
    𝘉 stands for bomb; the bombs are much bigger,
    So, brother, do not be too fast on the trigger.
   
    𝘚 stands for secret; you can keep it forever
    Provided there's no one abroad who is clever.
   

   Edward Teller had two children, Paul (1944?) and Wendy (31 August 1946); Wendy is not mentioned, so the alphabet was begun before August 1946. (Teller had been working on the 'Super' design before then, so 'H' could've been in it and part of the material Laura Fermi omits in her quote.)

3. Alamogordo Daily News, from Alamogordo, New Mexico; pg5 of 14 November 1957 (using the text transcript so uncertain if the letters are italicized in the original newspaper):

   Atom Alphabet

   Edward Teller, atomic scientist who is on the cover of Time magazine this week [see later], has somewhat of a lighter talent for verse. The following is his atomic alphabet which he created for his two youngsters:

    A stands for atom; it is so small
    No one has ever seen it at all.
    B stands for bombs; the bombs are much bigger.
    So, brother, do not be too fast on the trigger.
    F stands for fission; that is what things do
    When they get wobbly and big and must split in two.
    And just to confound the atomic confusion
    What fission has done may be undone by fusion.
    H has become a most ominous letter;
    It means something bigger, if not something better.
    S stands for secret; you can keep it forever —
    Provided there's no one abroad who is clever. 
   

4. Drawing Theories Apart: The Dispersion of Feynman Diagrams in Postwar Physics, Kaiser 2009 states:

   54. Teller's handwritten poem [on mesons], n.d., may be found in HAB, Folder 12:35. Teller was fond of composing such rhymes; see "Dr. Teller's Atomic Alphabet", reproduced in Anon., "Defense" (1957), 22.

   There is a DoD journal named Defense (ISSN: 0737-1217) but online access only goes back to 1994, and the catalogue entries claim it only started publication in 1980: "Imprint varies: Arlington, Va., Jan. 1980-Apr. 1987; Alexandria, VA, May 1987-, Bimonthly, 1986-", so I can't trace it any further, especially without better citation information ('22' probably refers to the volume, but what is the page number and why don't libraries know about any 1957 activity? Is there some sort of classification issue? Or does "Defense" not even refer to the journal Defense but something else entirely?) It may be the original source for the Alamogordo Daily News version.

5. Alternatively, "Defense" here may refer to the Time article mentioned in the Alamogordo article: "Knowledge is Power", Time. 11/18/1957, Vol. 70 Issue 21, p23. 7p:

   Multiple Monomania. With all this, plus university duties as an associate director of the Radiation Laboratory and a teacher of postgraduate physics. Teller's life shows scant resemblance to the stereotype of the scientist at work, insulated from the clamors and interruptions of the outside world. Even before Teller leaves his garden-girdled house in Berkeley in the morning, his harried secretary usually puts through two or three long-distance calls. After he gets to his office, a train of thought about some theoretical problem in nuclear physics is likely to be interrupted by a query from the Pentagon or a reminder that it is time to leave for the San Francisco airport to catch an outgoing plane. On his trips to the AEC's Livermore lab, 45 miles from Berkeley, Teller dictates letters to his secretary while driving. It is no wonder that Teller has not found time to finish the atomic alphabet (see box) that he started writing for his two youngsters.

   But the citation info doesn't quite match up (the article title is different and it's unclear what '22' refers to). The scans of the Time online version show that the atomic alphabet is the same version as the Alamogordo one.

6. Season 7, episode 2 "A is for Atom, B is for Bomb" of NOVA (22 January 1980) may have included it. Bulletin of the Atomic Scientists May 1980 says "it opens with nursery rhymes about nuclear weapons". It is not available to watch on the NOVA website or available on the Pirate Bay.

7. "Secrecy in Science : Adopting a Policy of Openness as the First Step Toward : Disarmament Would Strengthen Our Relationships With : Our Allies and Illustrate the Advantages of Freedom", "From nuclear physicist Edward Teller's recently published book, Better a Shield Than a Sword: Perspectives on Defense & Technology"

   After many months of political inaction following Hiroshima, the United States presented the Baruch Plan to the United Nations: The United States would share the secrets of nuclear energy in exchange for all nations agreeing to international control of nuclear power. The plan failed--the Soviets were not interested. That is not surprising, considering that they had probably already guessed our atomic secrets. As I wrote in an atomic alphabet for my young son: "S stands for secret; you can keep it forever. / Provided there's no one abroad who is clever." But the practice of classification continued; it was our "security," whether it worked or failed.

8. Conversations on the Dark Secrets of Physics, Edward Teller, Wendy Teller, Wilson Talley 1991; "Epilogue: After the Revolution", pg215-216 (the quote is sometimes misattributed to Wendy Teller, eg in Gaither's Dictionary of Scientific Quotations):

   ...The theory of nuclear structure remains incomplete because the nature and precise behavior of nuclear forces remains unknown.

   That did not prevent a semi-quantitative explanation of the behavior of nuclei. The practical results of that were the discovery of how to use nuclear fission and nuclear fusion. The first occurs in the heaviest nuclei, where repulsion between protons renders the nuclei unstable. The second is important for light nuclei and is responsible for energy production in the sun and other stars. It has been reproduced on earth on a small experimental scale as well as on a large scale.

   In trying to explain the facts of nuclear physics to my very young son, I attempted to compose an atomic alphabet, which is yet to be completed, although my son is no longer young. But I did write the rhyme for the letter F:

    F stands for fission
    That is what things do
    When they get wobbly and big
    And must split in two.
    And just to complete
    The atomic confusion,
    What fission has done
    Can be undone by fusion.*
   

   Our present knowledge of nuclei is in a very rough sense similar to knowledge of the behavior of molecules during the last century. Like the chemists of that period, we have crude, practical explanations but no systematic understanding.

   * WT: Can it really be undone?

   ET: No. The conclusion is based on poetic license, which in this place is entirely impermissible. Fission is for the big nuclei; fusion is for the small.

9. "COLD WAR Chat: Edward Teller, U.S. physicist", 21 March 1999:

   Chat Participant: Mr. Teller, what is your opinion of the recent allegations of China stealing nuclear secrets?

   Edward Teller: Half a century ago I wrote an atomic alphabet. I'll recite the first two lines: A stands for atom, it is so small no one has ever seen it at all. B stands for bomb, the bombs are much bigger, so brother do not be too fast on the trigger.

   [The relevant line is:] S stands for secret, you can keep it forever -- provided there is no one abroad who is clever. It is remarkable that atomic secrets have kept this long. What the Chinese know, probably they have invented it themselves. But I cannot be sure. That is a real possibility.

10. "Dr. Edward Teller: The Right Stuff" (interview by Jim Clash; excerpted from the 2003 book, Forbes To The Limits: Pushing Yourself to the Edge In Adventure and in Business, ch7 "Adventures in Physics and Metaphysics", "Edward Teller: Father of the Hydrogen Bomb", pg 180-193; unspecified date other than Teller is in his "mid-90s" and Teller was 95 in 2003; no additional material mentions the alphabet)

    Q: How did India and Pakistan get the atom bomb?

    Edward Teller: A half-century ago, I tried to write an atomic alphabet: “A” stands for atom -- it’s so small, no one has ever seen it at all. “B” stands for bombs -- the bombs are much bigger, so let’s not be so fast on the trigger. Do you know what “S” stands for?

    Q: Safety?

    ET: “S” stands for secret -- you can keep it forever, provided there’s no one else who is clever. India and Pakistan know that two and two makes four. You cannot keep scientific knowledge your own secret. We are the only ones clever enough to do it, right? If others have done it, they must have copied us. Maybe, but I doubt it.

11. "Edward Teller, a Fierce Architect of the Hydrogen Bomb, Is Dead at 95", 11 September 2003:

    For all that, he exerted great influence on government policy, his advice sought by Presidents Richard M. Nixon, Ronald Reagan and the first President George Bush as well as Nelson A. Rockefeller, the governor of New York who later became vice president under Gerald R. Ford. To many who studied under him, he was a hypnotic lecturer and teacher, particularly for the uninitiated. He loved children and once wrote a rhyming alphabet that hinted at his ambivalence over the hydrogen bomb, roughly a thousand times more powerful than its atomic predecessor.

     A stands for atom; it is so small
     No one has ever seen it at all.
     B stands for bombs; the bombs are much bigger.
     So, brother, do not be too fast on the trigger.
     F stands for fission; that is what things do
     When they get wobbly and big and must split in two.
     And just to confound the atomic confusion
     What fission has done may be undone by fusion.
     H has become a most ominous letter;
     It means something bigger, if not something better. 
    

12. VicXnews, 2011, unspecified sources:

    btw still looking for a copy of Tellers poem A is for Atom but can only find part of it...all are welcomed to help complete it(with Tellers words please) =8-)

    A stands for atom; it is so small
    No one has ever seen it at all.
    B stands for bombs; the bombs are much bigger.
    So, brother, do not be too fast on the trigger.
    F stands for fission; that is what things do
    When they get wobbly and big and must split in two.
    And just to confound the atomic confusion
    What fission has done may be undone by fusion.
    H has become a most ominous letter;
    It means something bigger, if not something better.
    Edward Teller's "Alphabet for the Atomic Age"
    

So in summary, the title is apparently "Atom Alphabet", it was principally written by 1946 for his son Paul (not Wendy), the most complete version I've found is the 1957 Alamogordo Daily News version, and probably the only letters Teller completed were 'A', 'B', 'F', 'H', and 'S' with no indications of any longer versions somewhere in Teller's private papers or something like that and specific indication that it was never finished (he wrote in the book of it, "which is yet to be completed", and it's unlikely he finished it within his remaining decade).

I've added the full version to Wikiquote to make it more easily findable.