So if this Robert is the right one, he was perhaps hard to find because
1. No baptism for him (online at least), though there are baptisms of his older siblings.
2. In 1841 he is recorded for some reason as Bellus, or similar, and transcribed as such on ancestry.
Though, if it is the same person, he is Bell in 1851, and enumerated as son of Ann.
Or, because of all that, I suppose you could look at another way, and wonder if Robert really was the son of Thomas and Ann?

Could he have been a son of the Elizabeth "Bellus" who may have been Bell, that we see in 1841, maybe she was some kind of relative of Thomas, and Robert stayed with them, and then with the widowed Ann. And thus gave Thomas Bell as his father when he got married to Isabella.
Not sure that is at all more likely, but, just in case, throw in a baptism at Tynemouth, 2 Nov 1834 as a possibility.
Robert Spurrier, son of Elizabeth Bell, Singlewoman.
Abode Little Bedford Street
https://www.freereg.org.uk/search_records/5dff9060f493fdae13facd9cBut
Elizabeth would have been very young. if she was 20-24 in 1841.
It may not be the same pair who are in Seaton Delaval in 1841. And anyway Bellus may not be a mistake for Bell (what name is it meant to be though?)
All very puzzling.