Unfortunately, I believe three of them (David, Mary Ann, and James) died before the 1841 census: I have the Bristol burials CD for the time period and found burials for David and Mary Ann in St Augustine, and James in St Phillips and Jacob (where he lived and baptised his children), all at an age that seems reasonable. I haven't been able to find any one of them in any of the censuses.
This is really annoying, since I'm trying to narrow down the parents of my ancestor Mary Ann Hill. She was the daughter of either David and Mary Ann (my personal favourite: if this is her she named two of sons, Edward and Frederick, after her brothers) or John and Jane (haven't even found a marriage for them). For that matter, I haven't been able to find most of their children in the censuses, and no burials for them either. There's only a few that I'm certain about, with no other members of their family living with or near them.