Wuss in mummy's pocket primarily? (4)
I believe the answer is:
wimp
'wuss' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
(Other definitions for wimp that I've seen before include "Informally, an ineffective man" , "Puny, pathetic individual" , "Weak-willed person" , "one of the Tory wets?" , "Namby-pamby" .)