Firm as aunts may be with a child (7)
I believe the answer is:
staunch
'firm' is the definition.
(I've seen this before)
'aunts may be with a child' is the wordplay.
'may be' is an anagram indicator.
'with' means one lot of letters go next to another.
'a child' becomes 'ch' (abbreviation for child).
'aunts' is an anagram of 'staun'.
'staun'+'ch'='STAUNCH'
'as' acts as a link.
(Other definitions for staunch that I've seen before include "Firm; stem" , "Loyal and dependable - stem the flow" , "solid" , "Reliable" , "Trustworthy" .)