Strange child, with better than even chance (4-2)
I believe the answer is:
odds-on
'better than even chance' is the definition.
(I've seen this before)
'strange child' is the wordplay.
'strange' becomes 'odd' (I've seen this before).
'child' becomes 'son' (male child).
'odd'+'son'='ODDS-ON'
'with' is the link.
(Other definitions for odds-on that I've seen before include "With success more likely as bookie would calculate" , "Better than evens" , "Very likely to happen" , "With success more likely than favour in bookie's phrase" , "A better than even chance of success" .)