Lump performing surgery on child's toy (6)
I believe the answer is:
dollop
'lump performing' is the definition.
'dollop' can be an answer for 'lump' (I've seen this in another clue). I'm not sure about the 'performing' bit.
'surgery on child's toy' is the wordplay.
'surgery' becomes 'op' (short for operation).
'on' says to put letters next to each other.
'child's toy' becomes 'doll' (I've seen this before).
'op' after 'doll' is 'DOLLOP'.
Can you help me to learn more?
(Other definitions for dollop that I've seen before include "Small measure, of mash say" , "Small shapeless mass" , "Large spoonful" , "Shapeless mass of soft food" , "Inelegant helping (of)" .)