It can only be conjecture, but I have heard of cases where a child has been on death's door and a younger newborn sibling has been named in their honour before they have actually died.
A long shot, I know - but if you check the death records of Thurgarton around the time the younger William died, you may find that there was an epidemic of some sort at the time.
On second look, there actually appear to be three Williams!
The William in the middle must have died early.
The Gent on the end was listed as only son and heir in his father's will, yet the William with the children was married about 10 years later, so they must be the same William.
There seems to be a bit of confusion though, as Robert on the left is listed as eldest son in 1754, which does not tally with the "Only son and heir" comment for William Gent above. All of the comments regarding "living in 1754" and "eldest in 1754" are likely related to the will of uncle John in 1754 which could shed some light on the situation. This will probably be at the Norfolk Record Office.
There's a chance that there is a generation missing or messed up here.The pedigrees are probably not that different from our modern One World tree - useful but errors do happen.
I would go to the actual registers if I were you as well (they are probably on the FamilySearch website with the other Norfolk registers).
