Pet dragon repaired by one supposed to have child's interests at heart (9)
I believe the answer is:
'one supposed to have child's interests at heart' is the definition.
(a godparent guides a child through life)
'pet dragon repaired' is the wordplay.
'repaired' is an anagram indicator.
'petdragon' anagrammed gives 'GODPARENT'.
'by' is the link.
(Other definitions for godparent that I've seen before include "Baptism sponsor" , "Pet dragon (anag)" , "Religious guardian" , "as one responsible for charge" .)