Taking one child to the concert (6)
I believe the answer is:
unison
'the concert' is the definition.
(to work in concert is to work in unison)
'taking one child' is the wordplay.
'taking one' becomes 'uni' (I can't explain this - if you can you should believe this answer much more).
'child' becomes 'son' (male child).
'uni'+'son'='UNISON'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for unison that I've seen before include "Simultaneous utterance" , "Concordance" , "using same pitch" , "Simultaneous action" , "In agreement - like sound of choir" .)