I think your original post was "I've just found out that I have an ancestor that died at 21 months at Seldom Seen, Newfield. My question is, does this place still exist?
Is there a church there where there may have been a burial?"
If you have not already paid it a visit you might like to go to
https://www.durhamrecordsonline.com. It has burial records for some churches in the Bishop Auckland area of County Durham.
https://durhamdiocese.org/ may also help you to find a church where the burial could have taken place. Churches that were near Newfield included Whitworth Parish Church and Binchester Church - relatives including my Mum are buried in Binchester's graveyard.
In the 1940s my father was the Colliery Manager of Leasingthorne Colliery and had oversight of the Coal Mine at Newfield.