Given he is in the same place as 1861 I'd say son of William & Susan was a dead cert.
William died and in 1861 Susan has children listed Westbury until William 16, who is Wells. That is also true in 1851, but I don't think there is much doubt. After all in 1861 his birthplace is unknown. He is only 2 years older than William and Wells, Wookey and Westbury are all in the same registration district.