Doctrine kids read endlessly (4)
I believe the answer is:
idea
'doctrine' is the definition.
(thesaurus)
'kids read endlessly' is the wordplay.
'kids' becomes 'id' (I am not sure about this - if you are sure you should believe this answer much more).
'endlessly' says to take the centre (the ends of the words are removed).
The middle of 'read' is 'ea'.
'id'+'ea'='IDEA'
Can you help me to learn more?
(Other definitions for idea that I've seen before include "Purpose" , "Thought, belief" , "Proposal" , "Intention" , "Aim" .)