Firm as aunts may be with a child (7)
I believe the answer is:
staunch
'firm' is the definition.
(I've seen this in another clue)
'aunts may be with a child' is the wordplay.
'may be' indicates an anagram.
'with' is a charade indicator (letters next to each other).
'a child' becomes 'ch' (abbreviation for child).
'aunts' anagrammed gives '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" .)