Hello all who have helped me with this query,
I have since found them on the 1841 census, thankyou. I still know very little about my Grace Harrison, the unknown child was Mary Ann but she seems to have disappeared after this, no death can be found so maybe she was adopted out. Grace had a son, John in 1846 ( also while unmarried ) & yes she is living with her brother William & his family in 1851. On John's birth cert it gives Grace's place of residence as Lewisham workhouse but John was born at William's house in Sydenham. I cannot find Grace after this date.
Grace's mother Maria died (perhaps of exhaustion) & her father remarried a woman 32 years younger than him & in total, that I can find, William had 17 children, he died age 83.
Thanks once again,
Meredith