A childish story? (3)
I believe the answer is:
fib
'story?' is the definition.
('fib' can be a synonym of 'story')
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for fib that I've seen before include "minor piece of fiction" , "Story" , "Petty falsehood" , "Little white lie" , "Small lie" .)