Has young girl at last entered grottos? (6)
I believe the answer is:
calves
'has young' is the definition.
('calve' can be a synonym of 'have young')
'girl at last entered grottos?' is the wordplay.
'at last' indicates one should take the final letters.
'entered' means one lot of letters goes inside another.
'grottos?' becomes 'caves' (grotto is a kind of cave).
The final letter of 'girl' is 'l'.
'l' inserted inside 'caves' is 'CALVES'.
(Other definitions for calves that I've seen before include "Backs of legs" , "Young domestic cattle" , "features of legs" , "Bovine young - parts of leg" , "Young farm animals" .)