Briefly visits small room with son among relatives (5,2)

'briefly visits' is the definition.
(to look in on someone is to briefly visit them)

'small room with son among relatives' is the wordplay.
'small room' becomes 'loo'.
'with' is a charade indicator (letters next to each other).
'son' becomes 's' (genealogical abbreviation for son).
'among' means one lot of letters goes inside another (inserted letters are placed among others).
'relatives' becomes 'kin' (kin can mean relatives or family).
's' put inside 'kin' is 'ksin'.
'loo'+'ksin'='LOOKS IN'