Baby son going to shops (5)
I believe the answer is:
small
'baby' is the definition.
(thesaurus)
'son going to shops' is the wordplay.
'son' becomes 's'.
'going to' means one lot of letters go next to another.
'shops' becomes 'mall'.
's'+'mall'='SMALL'
(Other definitions for small that I've seen before include "tiddly" , "Of little size" , "Itsy-bitsy" , "Of no great size" , "Tiny" .)