Good score for child’s term for flier (6)
I believe the answer is:
birdie
This clue is a double definition.
'good score' is the first definition.
(good score in golf)
'child's term for flier' is the second definition.
(childish term for a bird, something which flies)
'for' acts as a link.
(Other definitions for birdie that I've seen before include "One watched" , "One under par - watch it!" , "Good hole" , "One under in 20 across" , "Golf score of one stroke under par" .)