Hi again Lu,
Yes, like you I'd think that Mary Ann, christened 1843, is the Mary Ann said to be aged 1 on the 1841 passenger list. Especially as we found a christening for Jane Elizabeth (age 3 on the passenger list) in London but not one for Mary Ann, and that Mary Ann isn't with the family in the 1841 census, and that we couldn't find a registration of her birth in England.
Genni's 'Marion' is surely Mary Ann (note her given name on the birth of James BALLI). And ages on death certs are notoriously unreliable! Perhaps, after the death of John BALLI, when she presumably re-married to a Mr CALDWELL, he might have been a younger man and she might have told a little fib - not unknown

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From the information on the NSW State Records site
http://www.whitepages.com.au/wp/initResSearch.doit seems that the Orphan Schools were for needy and destitute children as well as actual orphans. And remember that both parents were named on the Petition so they must have been alive at the time.
As for George, who knows ... Perhaps the age at death on the index is wrong ...
I guess that many of the questions could be answered by purchase of all the certificates and other documentation. But that might mean that you would end up destitute

JAP