Many thanks everybody.
I now know that Thomas and Amy had 6 children, not 5 as I originally thought.
Charlotte, b. 1835 and seems to have died a few days later.
James, b. 1837. I can't find him after the 1861 census, where he is working as a carter at Granhill Farm, Sparsholt, Berks.
Sarah Ann, b. 1839 and died in 1858.
Eleazar, b. 1841 and was poisoned by his father in 1844.
Henry George, b. 1843 and died at the same time as Eleazar, possibly poisoned by his father also.
Charlotte, b. 1845. married William Rose in 1882. There are 4 children in the 1881 census, William b. 1871, Arthur b. 1873, Annie b. 1876 and Evan b. 1879. all with the surname Rose. But from Free BMD only one is registered as Rose, the other 3 are as Jennings. Even though William is described in the census as a widower, there is a good chance that all 4 were conceived before William and Amy were married. Charlotte died in 1891 and William in 1900, both Newbury reg. district.
Amy Jennings, nee Flitter, went on to marry Charles Bryant in 1861 and died in 1884 in Thatcham. Charles died before her in 1879.
The Seymore child, in the 1841 census, was Joan Seymore, Thomas's niece, who, at his trial, he tried to blame for the death of Eleazar.
Dave