One with children - on average, maybe ten? (6)
I believe the answer is:
parent
'one with children' is the definition.
(I've seen this before)
'on average maybe ten?' is the wordplay.
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'average' becomes 'par' (average score in golf).
'maybe' indicates anagramming the letters.
'ten' with letters rearranged gives 'ent'.
'par' put within 'ent' is 'PARENT'.
(Other definitions for parent that I've seen before include "Begetter of offspring" , "person responsible for children" , "Immediate ancestor" , "a dam, perhaps" , "old man?" .)