... helps son wearing wellies, perhaps (6)
I believe the answer is:
boosts
'helps' is the definition.
(boost is a kind of help)
'son wearing wellies perhaps' is the wordplay.
'son' becomes 's'.
'wearing' means one lot of letters goes inside another.
'wellies perhaps' becomes 'boots' (Wellington boots).
's' inserted inside 'boots' is 'BOOSTS'.
(Other definitions for boosts that I've seen before include "Pushes or thrusts upward like a rocket" , "Pushes or shoves upward" , "Pushes upward or increases" , "Increases or improves" , "Pushes or thrusts upwards, say a rocket" .)