They crow of child’s gag about rector (9)

'they' is the definition.
Both the definition and answer are plural nouns.
Maybe you can see an association between them that I don't see?

'crow of child's gag about rector' is the wordplay.
I cannot quite understand how this works, but
'crow' could be 'brag' ('brag' can be a synonym of 'crow') and 'brag' is found within the answer.
'about' could be 'a' (abbreviation in Chambers) and 'a' is located in the answer.
'rector' could be 'r' and 'r' is present in the answer.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?