Hard work put an end to childish game (9)
I believe the answer is:
hopscotch
'childish game' is the definition.
'hopscotch' can be an answer for 'game' (hopscotch is a kind of game). I'm not certain of the 'childish' bit.
'hard work put an end to' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'work' becomes 'op' (short for opus).
'put an end to' becomes 'scotch' (I've seen this before).
'h'+'op'+'scotch'='HOPSCOTCH'
Can you help me to learn more?
(Other definitions for hopscotch that I've seen before include "Traditional children's game" , "Jumping game" , "Children's game with squares on ground" , "child's play" , "Playground game" .)