Room the child, a boy, is to occupy (5)
I believe the answer is:
salon
'room' is the definition.
(salon is a kind of room)
'the child a boy is to occupy' is the wordplay.
'the child' becomes 'son' (son is a kind of child**).
'a boy' becomes 'al'.
'is to occupy' is an insertion indicator.
'son' going around 'al' is 'SALON'.
(Other definitions for salon that I've seen before include "Reception room in grand house" , "(Room for) gathering of distinguished people" , "Reception room - social gathering" , "Literary gathering" , "Room where beautician works" .)