Male finally beats children's game (4)
I believe the answer is:
stag
'male' is the definition.
(I've seen this before)
'finally beats children's game' is the wordplay.
'finally' says to take the final letters.
'children's game' becomes 'tag' (I've seen this before).
The final letter of 'beats' is 's'.
's'+'tag'='STAG'
(Other definitions for stag that I've seen before include "This party is for men only" , "Antlered beast" , "party given by Uncle Sam" , "Game - speculator" , "speculator wanting quick profit" .)