Think logically about a child (6)
I believe the answer is:
reason
'think logically' is the definition.
(synonyms)
'about a child' is the wordplay.
'about' becomes 'rea' (I've seen this in other clues).
'a child' becomes 'son' (male child).
'rea'+'son'='REASON'
(Other definitions for reason that I've seen before include "Justification (for action)" , "Cause, justification" , "use of wit" , "Ability to think rationally" , "Cause for sanity" .)