Where youngsters may play with spades alongside mine (7)
I believe the answer is:
sandpit
'where youngsters may play' is the definition.
(children might play in a sandpit)
'with spades alongside mine' is the wordplay.
'with' becomes 'and'.
'spades' becomes 's' (abbreviation in card games).
'alongside' is a charade indicator (letters next to each other).
'mine' becomes 'pit' (down the pit).
'and' after 's' is 'sand'.
'sand'+'pit'='SANDPIT'
(Other definitions for sandpit that I've seen before include "Children's play area - it'd snap (anag)" , "place where youngsters can play" , "children may play here" , "Site of castle perhaps" , "Playground feature" .)