Old setter's good with child (9)
I believe the answer is:
expecting
'with child' is the definition.
(expecting a baby)
'old setter's good' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'setter' becomes 'pectin' (setting agent for jams etc.).
'good' becomes 'g' (abbreviation).
'ex'+'pectin'+'g'='EXPECTING'
(Other definitions for expecting that I've seen before include "pregnant" , "Regarding as likely to happen" , "Anticipating, looking forward to" .)