Girls of nine, perhaps, in a bus (7)
I believe the answer is:
bunnies
'girls' is the definition.
The answer and definition can be both people as well as being plural nouns.
Maybe they are linked in a way I don't understand?
'nine perhaps in a bus' is the wordplay.
'perhaps' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'nine' anagrammed gives 'nnie'.
'nnie' inserted inside 'bus' is 'BUNNIES'.
'of' is the link.
Can you help me to learn more?
(Another definition for bunnies that I've seen is " Rabbits".)