Cambs FHS has an excellent website at
http://www.cfhs.org.uk/Search.htmlI can't see a baptism of either John or Sarah in the Baptism Index though.
I also wonder if Elizabeth is his mother as she seems a bit on the old side, as 60 in 1841 means 60-64. Similarly James age 30 could have been 34 making him old enough to be the father of John and William
If you check the Burial Index there's a Jane Smith age 34 buried in 1835 in Lt Gransden, which may, or may not, be significant.
If you buy his 1864 marriage cert you'll get both fathers' names, and you'll also be able to confirm that Sarah wasn't also a widow and thus her maiden name would be something other than Webb.
Regards
David
Later - the reason I couldn't see Sarah in Cambs baptism index is, as it's just struck me, that Abbotsley was in Hunts - it wasn't until recently when Hunts was merged with Cambs and disappeared, that Abbotsley was in the county of Cambs. And as luck would have it Abbotsley is only Hunts parish register transcript that I have - the only Sarah Webb baptism that I can see was on 15 June 1834, dau of William & Susan, labourer. Also done on the same day were her brothers George and Joseph, so one or more of them look as though they were late baptisms. But you need to double check that the Sarah Webb who married John Smith wasn't a widow
