I’m returning cake, evenly cut, for boy (4)
I believe the answer is:
mick
'boy' is the definition.
(boy's name)
'i'm returning cake evenly cut' is the wordplay.
'i'm' becomes 'im' ().
'returning' is a reversal indicator.
'evenly cut' means one should take alternating letters (letters in even-numbered positions removed).
The alternate letters of 'cake' are 'ck'.
'im' written backwards gives 'mi'.
'mi'+'ck'='MICK'
'for' is the link.
(Other definitions for mick that I've seen before include "Take the - - out of" , "Diminutive of Michael" .)