Frightened son leaving to be looked after (5)
I believe the answer is:
cared
'be looked after' is the definition.
(I've seen this in another clue)
'frightened son leaving' is the wordplay.
'frightened' becomes 'scared' (scared means frightened or fearful).
'son' becomes 's' (genealogical abbreviation for son).
'leaving' indicates named letters should be taken away.
'scared' with 's' removed is 'CARED'.
'to' is the link.
(Other definitions for cared that I've seen before include "had feelings" , "Felt affection (for)" , "Tended" , "Was concerned" , "Felt concern or interest" .)