I've only read through this thread in a hurry so I've probably missed something, but isn't this family Jean's found the one you're after? William Henry Callow born 1851 son of Benjamin Callow could be the one in the 1851 census ("not christened" 1 week old) and in 1861 with grandfather aged 61 born IOM? Age 8 must be wrong if it's the same child that was 1 week, but the sister Mary Frances' age is out too - should be 12 not 11.