Barbara there is no baptism on the Vic Registry for
John c1850 however there are two baptisms for children Elizabeth and Samuel to Samuel and Jane at Christ Church, Geelong in 1850 and 2 births "F" and Emma registered to Samuel and Jane HOWARTH at Colac in 1855 and 1857 respectively. Jane died in 1859.
May I ask the source of your information about John?
Either of the birth registrations should give all previous births to the marriage.
I suggest you trawl the
DUCK entries on these databases. Further information available. Details on website.
http://zades.com.au/gandd/index.php/databases/gddbsMentions of a John in the Birregurra Court.
Cando