In snug surroundings, expert with child (5)
I believe the answer is:
sprog
'child' is the definition.
(informal term for a child)
'in snug surroundings expert' is the wordplay.
'in' means one lot of letters goes inside another.
'snug surroundings' becomes 'sg' (I can't explain this - if you can you should give a lot more credence to this answer).
'expert' becomes 'pro' (short for professional).
'sg' placed around 'pro' is 'SPROG'.
'with' acts as a link.
Can you help me to learn more?
(Other definitions for sprog that I've seen before include "Infant" , "Child; recruit (mil. slang)" , "Kid" , "Baby (slang)" , "little one" .)