James Drain, son of David & Jean (Hayslet) Drain married the first time to Nancy Standoff 26 Oct 1831 in Rockbridge Co, VA. She died about 1875. James remarried another woman named Nancy in 1876. She was born Nancy Porter and was the widow of a Mr. Black.
Nancy Standoff was alone with kids in 1870 probably because James was travelling at the time the census was taken that year. He did that a lot. Half of his family had gone to either Illinois or West Virginia by that time and visited them (without his family) quite often. (I descend from the West Virginia group).
Jean Hayslet died in 1855 in Illinois (she and David moved there in the 1840's). Not sure why she is not represented in the 1830 census. Do keep in mind the Census records are very very inaccurate.
James's dau, Mary, was called Polly and married 7 Nov 1863 in Rockbridge Co to Lewis Hostetter (1838 - 1880) son of David Hostetter & Jane Hughes
James' dau, Margaret, married 1 Feb 1872 in Rockbridge Co, James Boley (b.ca.1844) son of John & Amelia Boley
As for John and Charles who are small children in 1870, I am not sure of their connection. But there is a son of James and Nancy who died rather young, I don't know when. His name was William (b.ca.1833) and could be their father. It is quite possible he married say 1861 and was dead by 1870 leaving these two children behind. I have not been able to find him on the 1870 census.