Son with cap going back to play area (7)
I believe the answer is:
sandpit
'play area' is the definition.
(I've seen this before)
'son with cap going back' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'with' becomes 'and'.
'cap' becomes 'tip' (both can mean the top of something).
'going back' shows that the letters should be reversed in order.
'tip' in reverse letter order is 'pit'.
's'+'and'+'pit'='SANDPIT'
'to' is the link.
(Other definitions for sandpit that I've seen before include "children may play here" , "Excavation for children to play in" , "Play area; quarry" , "place where youngsters can play" , "Site of castle perhaps" .)