I would rephrase that. Didn't you already pass ownership on to your children? If the totalitarians pass a law forbidding transfers of firearms within the family without a background check, it would be nice to have a letter dated today or at the earliest age your kids were permitted to own (not purchase, which is often older) firearms. That letter could be passed on when you later transfer custody of their firearms.
Do I just put all, or itemize in the letter? Then what, have it notarized?