John was born in Alton, Staffs, and according to the 1851 census, Mary was born in Tatenhill, near Burton upon Trent, though no baptism records can be found which confirm this. With Mary being recorded as 43 in 1841 and 55 in 1851 several possible records for Mary's baptism are ..
    - at Leek, Jan 1798 (parents John/Elizabeth)         - at Mapleton, July 1799 (parents James/Sarah)
Mary had married George Udall in 1819 (in Derby) - they had 3 children (William, Martha & Mary). George died in 1826. Mary also had an illegitimate child (David) in 1829 - baptised in Ellastone. David's marriage certificate, however, gives George as his father.
John and Mary married at Derby in 1834. Because Mary spent her early married life around Ashbourne, Derbyshire (William, Martha & Mary Udall were all baptised at Bradley, and Charles Forester at Osmaston), I feel that James & Sarah are more likely to be Mary's parents, Mapleton being only about 2 km from Ashbourne.
By the time Thomas was born John and Mary were living at Burton upon Trent.
Charles' marriage certificate (1871) indicates John was a gamekeeper, though he was no longer living at that time.