Help a son that’s lost outside US city (2,4)
I believe the answer is:
el paso
'us city' is the definition.
(city in Texas)
'help a son that's lost outside' is the wordplay.
'that's lost outside' indicates a hidden word (letters from outside are removed).
'EL PASO' can be found hidden inside 'help a son'.
(Other definitions for el paso that I've seen before include "city on Mexican border" , "West Texas town" , "US city" , "Texan city" , "City of Texas on the Rio Grande; aslope (anag.)" .)