Fiction prompt: Pick a core memory from childhood (sub ~8 y/o) and describe it in the way a child would recount it. If details are missing, make them up.
Poetry prompt: Take something peculiar that adults do and describe it from the perspective of a child.
Non-fiction prompt: When did you feel you were no longer a child? When did you feel like you had become an adult?

There is no greater agony than bearing an untold story inside you.