Boys and girls initially pack (3)
I believe the answer is:
bag
'pack' is the definition.
(I know that bag is a more specific form of the action pack)
'boys and girls initially' is the wordplay.
'initially' says to take the initial letters.
The first letters of 'boys and girls' is 'BAG'.
(Other definitions for bag that I've seen before include "Gladstone, for example" , "Container for carrying thing" , "Valise" , "Pouch" , "interest" .)