Wicket in children's game is part of branch (4)
I believe the answer is:
twig
'is part of branch' is the definition.
(I've seen this before)
'wicket in children's game' is the wordplay.
'wicket' becomes 'w'.
'in' is an insertion indicator.
'children's game' becomes 'tig'.
'w' placed inside 'tig' is 'TWIG'.
(Other definitions for twig that I've seen before include "Small piece of wood" , "Suddenly realise" , "Division of branch" , "Small part of a branch - suddenly understand" , "Small tree shoot" .)