It's not played by present schoolchildren (6)
I believe the answer is:
truant
'present schoolchildren' is the definition.
Both the definition and answer are adjectives. Perhaps there's an association between them I don't understand?
'it's not played' is the wordplay.
I cannot quite understand how this works, but
'not' could be 'nt' (synonyms) and 'nt' is present in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
This explanation may well be incorrect...
'by' is the link.
Can you help me to learn more?
(Other definitions for truant that I've seen before include "Academic absentee" , "Child bunking off school" , "Pupil absent without permission" , "Wandering" , "On the mitch" .)