Hi,
Welcome to RootsChat

I found this which has a bit more info about John,
New South Wales, Australia, Assisted Immigrant Passenger Lists, 1828-1896
John MOSS
Married male Immigrant
Arrival by the Bossonah Merchant
Brought out by Alex CAMPBELL
A native of Birch Essex, son of Joseph a labourer dead. & Mary HODGES his wife there.
Calling Agricultural Labourer
Age on Embarkation 37years 29th December 1840
Persons certifying registry of baptism: J HOLMES
Character and Person certifying the same: W PALMER, J WALKER
State of bodily health, strength and probable usefulness: V Good
Religion: Protestant
Comments: Reads and writes
ooh next pages have info about about Mary and the children.....
Mary MOSS
Married Female Immigrant
A native of Legsden, Essex, daughter of William DRAIN a labourer dead and Sarah Ann also dead
Calling: Domestic Servant
Age: 39 29th September 1840
Persons certifying registry of baptism: J HOLMES
Character and Person certifying the same: Same as Husband
State of bodily health, strength and probable usefulness: Very Good
Religion: Protestant
Comments: Reads only
Male Children exceeding one and under eighteen
Joseph 14 years 27th December 1840
Robert 12 years 12th March 1840
Thomas 11 6th May 1840
___________
R MOSS 10yrs of age at time of application October 26? 1840
Persons certifying registry of baptism: None
I think I've transcribed this correctly, I think Legsden might be Lexden and I don't know why R MOSS is written differently to the other children.
If I'm understanding the above info then John would have been born 29th December 1803 so here is a possible baptism for John, about 3.5 miles from Birch, Essex.
29 Jan 1804
Copford, Essex
John MOSS
Parents: Joseph & Mary
Marriage23 Nov 1834
Birch, Essex
John MOSS
Mary DRANE
That would mean all the above children were not John and Mary's.
I'll go and look for them.
Regards,
Daisy