Child's play that's presented at birthday party (5,2,4)
I believe the answer is:
piece of cake
I believe this is a double definition.
'child's play' is the first definition.
(synonyms)
'that's presented at birthday party' is the second definition.
(birthday cake)
(Other definitions for piece of cake that I've seen before include "one can sail through?" , "Part of Madeira perhaps" , "Easy task" , "slice?" , "It's easy (to eat)" .)