Child's short note (4)
I believe the answer is:
chit
I believe this is a double definition.
'child's' is the first definition.
(thesaurus)
'short note' is the second definition.
(I've seen this before)
(Other definitions for chit that I've seen before include "Impudent girl" , "Note - voucher" , "Receipt; a child" , "Short official note recording a sum owed" , "Brief note" .)