Kid endlessly adjusted screen time on the sly (2,6)
I believe the answer is:
in secret
'on the sly' is the definition.
(synonyms)
'kid endlessly adjusted screen time' is the wordplay.
'endlessly' says to take the centre (the ends of the words are removed).
'adjusted' indicates anagramming the letters.
'time' becomes 't' (abbreviation).
The middle of 'kid' is 'i'.
'screen' is an anagram of 'nsecre'.
'i'+'nsecre'+'t'='IN SECRET'
(Other definitions for in secret that I've seen before include "privately" , "Not openly stated" , "Confidentially" , "sub rosa" , "Covertly" .)