No, son, go back! They are not allowed (2-3)
I believe the answer is:
no-nos
'no' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'son go back they are not allowed' is the wordplay.
I cannot really understand how this works, but
an anagram of 'son' is 'nos' which is present in the answer.
'not' could be 'no' (I've seen this in other clues) and 'no' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for no-nos that I've seen before include "Forbidden actions" , "Forbidden fruits" .)