Hi Sue,
I appologise for not responding, I should have because I have looked at this possibility.
I have a copy of a letter from the Home Office about the convict Sarah LYNCHEY which includes a note that convict mothers could take daughters to the age of 12 years and sons to 8 years whith them to OZZ.

The James you found would have been born C 1827 and would have been 8 when Sarah left for OZZ.

I do think that the son who went with her was named James, the lad sentenced with Sarah had some 20 tattoos detailed on the indent for the Mary Ann including one "brother James 1835"

I have also found details of the admission of a child James LYNCH aged 6 to the Male Orphan School in Sydney on 19/09/1835. Sarah had a5rrived on the MaryIII on 06/09/1835.

There is also an admission to the Female Orphan School of a Sarah LYNCH aged 7 and from the dissentor baptisms I think that she may have been one of the daughters of Sarah LYNCHEY. The other daughter was my GG grandmother.

So far as the identity of the son left behind I have 2 possibilities so far.
Andrew LYNCHEY who married at Ballaugh in 1841 with the permission of his guardian William Quayle. I suggest that this makes hin about 20 with a birth C 1821 and therefore too old to accompany Sarah.
The other is a Charles LYNCHEY who is listed in the 1841 Census in Castletown aged 25, he would have been born C 1816 and therefore too old to travel with Sarah.
I have found births and marriaged descending from Andrew but nothing on his parents. I am yet to find furthe info on Charles.

Thank you for your info.

Cheers
Peter
Melbourne