searched: Wikipedia, google - 'Hiroshima' 'survivor' 'aging/ageing' 'children' 'maturity' in various combinations, but I can only find articles about cancer rates among survivors and their children.
I want to know whether a child survivor of Fat Man or Little Boy would have a retarded maturation process, or even be 'frozen' at a certain age. I'm trying to confirm or deny something I vaguely remember from a book when I was in primary school. It's about a little girl who survives the bombing of Hiroshima or Nagasaki, and a particular line that really stuck with me reads 'she grew old, but she never grew up. It was because of the bomb, her mother said'.
Basically, my character is a kind of undead/angel mix, who died when the bomb hit. Everyone in this afterlife ages slowly, at different rates depending on where they are assigned to live, but in the time since the bomb he's only aged about two or three years - say, beginning to end of middle school - when everyone else in his sector who's been around that long has aged anywhere from five to ten. He's worried that he'll be stuck at 13 forever, or take several centuries to finish puberty. If the child survivors of the bomb had problems with ageing, it would add an extra fillip of worry, as in this world, some types of injury carry on into the afterlife.
EDIT: thanks to fancypony! The book I was thinking of was 'Hiroshima No Pika'. And while I don't think I quite got across what I really wanted to know, I figured it out from the answers, anyway. Thanks to everyone!