Well done, Yorkslass, for finding Thomas' baptism at Wiggenhall on 17/3/1790 - son of Thomas and Mary. FreeReg shows at least 4 possible siblings: William 1782, Frances c.1785-7 bur.31/5/1787,Mary 1788 and James 1798, bur.16/3/1798.
Suspect that father Thomas was married twice - first to a Mary Gooding 25/12/1781 at Watlington (next door to Wiggenhall) and that William 1782 was their son.
A Mary, wife of Thomas, buried 6/1/1783 Watlington (Watlington may well have been her birth parish), as was son William the same day. Thomas then married Mary Mitchel 25/1/1785 Wiggenhall and at least 4 children baptised there as shown above. 2nd wife Mary was buried at Wiggenhall on 27/2/1800.
Yorkslass' finding kind of answered my immediate thoughts - as events were all pre civil registration how did you know that Thomas bc.1790 was the son of a William and, equally so, that William bc.1751 had a son Thomas anyway. You can't even be sure that William himself was born in Norfolk.
So if Thomas 1790 is son of a Thomas this leads us to when/where Thomas senior was born.
Annette