I wonder if the census taker for the 1851 census made an error in entering the age for Thomas Gill son of James & Margaret. The age for Thomas clearly shown as 11 and both Lawson's and Ancestry (who also estimates the birth as Abt 1840) record this age. However, the 1861 census shows Thomas s/o James and Margaret Gill as 10. The age for the parents as well as the names and age for their children are consistent between the 1851 & 1861 census, so I'm inclined to think Thomas' age for the 1851 census should have been 1 not 11. This would also be consistent with an ca 1847 marriage date for James & Margaret.
Do you a source for James & Margaret marrying under the name Gale ca 1847?

On a related matter, do you have any record of Anne and Margaret Quine d/o Thomas & Isabella also having a sister named Elleanor. I have a marriage between an Elleanor Quine (d/o Thomas Quine) and Thomas Beckerleg, 6 July 1851. I believe their daughter Elizabeth Ellen Beckerleg is the cousin of Sophia Terzah Kermode, named as a cousin in the latter's 1916 will. The earliest census records 1841 & 1851 for Thomas/Isabella Quine, do not show an Elleanor which could be explained by being born abt 1824. An Isabella Rebecca Quine is also noted in the will.

Wayne