Absolutely tiny child with friend (7)
I believe the answer is:
totally
'absolutely' is the definition.
(synonyms)
'tiny child with friend' is the wordplay.
'tiny child' becomes 'tot' (term for a young child).
'with' means one lot of letters go next to another.
'friend' becomes 'ally' (an ally is a friend or supporter).
'tot'+'ally'='TOTALLY'
(Other definitions for totally that I've seen before include "Altogether" , "Completely, entirely" , "without reserve" , "to the nth degree" , "To the full extent" .)