The William of Daniel & Margaret was aged 6 months in the 1841 census, so born Dec/40 or Jan/41.

The only William born post 1841 in Jurby that I can find in the 1851 census is the son of William & Ann.
His age is given as 6, bp 18 Aug 1844, mother Ann Lord.

There is a baptism for a William at Jurby 21 Sep 1842 but only the mother's name is given - Margaret Cleator.