Pot for sale (not suitable for children) beside prison (4,3)
I believe the answer is:
toby jug
'pot' is the definition.
(Toby jug is a type of vessel)
'for sale not suitable for children beside prison' is the wordplay.
'for sale' becomes 'to buy' (something available to buy is for sale).
'not' indicates named letters should be taken away.
'suitable for children' becomes 'U' (Universal film certificate).
'beside' means one lot of letters go next to another (I've seen this in other clues).
'prison' becomes 'jug' (slang term).
'tobuy' with 'u' taken out is 'toby'.
'toby'+'jug'='TOBY-JUG'
(Other definitions for toby jug that I've seen before include "Type of mug" , "Figurine mug" , "Vessel shaped like a stout man" , "Drinking mug shaped as a stout man" , "cup" .)