Urgent call about new boys (4)
I believe the answer is:
sons
'boys' is the definition.
('son' can be a synonym of 'boy')
'urgent call about new' is the wordplay.
'urgent call' becomes 'sos' (an SOS message sent in an emergency).
'about' means one lot of letters goes inside another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'sos' going around 'n' is 'SONS'.
(Other definitions for sons that I've seen before include "Male offspring" , "DH Lawrence novel: __ and Lovers" .)