Clean up dog, perhaps, sweet little youngster (6)
I believe the answer is:
moppet
'sweet little youngster' is the definition.
'moppet' can be an answer for 'youngster' (I've seen this in another clue). I'm not sure about the 'sweet little' bit.
'clean up dog' is the wordplay.
'clean up' becomes 'mop' (I've seen this in another clue).
'dog' becomes 'pet' (dogs are often kept as pets).
'mop'+'pet'='MOPPET'
'perhaps' is the link.
Can you help me to learn more?
(Other definitions for moppet that I've seen before include "Little darling" , "Endearing small child" , "Endearingly sweet child" , "Tot" , "young child" .)