Think logically about a male child (6)
I believe the answer is:
reason
'think logically' is the definition.
(synonyms)
'about a male child' is the wordplay.
'about' becomes 'rea' (I've seen this in other clues).
'a male child' becomes 'son' (I've seen this in another clue).
'rea'+'son'='REASON'
(Other definitions for reason that I've seen before include "Cause or motive" , "Purpose" , "Cause - logic" , "The right exercise of the mind" , "Ability to think rationally" .)