Puzzling child, as favourite may be (4-2)
I believe the answer is:
odds-on
'puzzling child as favourite may be' is the definition.
I can't tell whether this definition defines the answer.
'puzzling child' is the wordplay.
'puzzling' becomes 'odd' (I've seen this in another clue).
'child' becomes 'son' (male child).
'odd'+'son'='ODDS-ON'
Can you help me to learn more?
(Other definitions for odds-on that I've seen before include "Bookie's assessment of success being more likely than failure" , "With success more likely as bookie would calculate" , "With success more likely than failure - check with bookie" , "With success more likely than favour - ask bookie" , "Rated likely to win" .)