Secret brother connects mother and child (5)
I believe the answer is:
mason
'secret brother' is the definition.
'Mason' can be an answer for 'brother' (Mason is an example). I am not certain of the 'secret' bit.
'connects mother and child' is the wordplay.
'connects mother' becomes 'ma' (I can't explain this - if you can you should believe this answer much more).
'and' means one lot of letters go next to another.
'child' becomes 'son' (male child).
'ma'+'son'='MASON'
Can you help me to learn more?
(Other definitions for mason that I've seen before include "He works with stone - may be free" , "Stone-worker" , "One is skilful with stone" , "One going to work in building" , "Builder in stone" .)