Firstly on the 1851 census John and Mary have a Whitaker Welburn as their son aged 4. The baptism for Whitaker Welburn on 19 Sep 1846 at Drax has his parents as John and Ann and John is a labourer. On his marriage on 13 Nov 1869 his father is John a bricklayer. Could the baptism record be a mistake?
The only way to know for sure is to see the birth certificate.
It could be the baptism record is not correct.
Also possible that Whittaker belonged to John and Ann, and he was taken in my Mary, because her sister was unable to look after him. In 1851 John and Ann had a child named Isabella who was born 14 Oct and died 3 days later. Then Ann was buried on 20th October.
Birth regoWELBREN, WHITTAKER Mother: WAUD
GRO Reference: 1846 D Quarter in SELBY Volume 23 Page 551
Secondly on the 1871 census John and Mary have a daughter Mary Jane aged 6 months. By the 1881 census she is a granddaughter and 1891 she is Johns niece. Who is Mary Jane?
I would say that Mary Jane is a grandchild, or rather, a grandniece. Birth certificate would clarify.
Birth regoWELBURN, MARY JANE - no mother recorded
GRO Reference: 1870 S Quarter in SELBY Volume 09C Page 624 Occasional Copy: A
When she married, Mary Jane said her father was George Welburn.