You might want to contact the profile manager of Ruben Ford and ask your question directly of him, he may have sources that will help you.
Below the profile details on Ruben’s profile page, on the left hand side, you will see a line that looks like this:
Profile manager: _________ [send private message]
If you click [send private message] you can directly email the profile manager.
Also, on the 1880 Census Ruben, aged 39 is listed with spouse Mary aged 24. As the oldest child is already 18 at this time, it appears that maybe Mildred died and this particular Ruben Ford remarried. I didn't find a see a death record for Mildred, so it's not possible to determine which of the younger children might or might not be children of Mary rather than Mildred.
From familysearch.org
U S Census, 1880 Bethlehem, Marshall, MS
self Reuben Ford M 39 MS
wife Mary Ford F 24 MS
son Willie Ford M 18 MS
dau Rocksie Ford F 14 MS
son Thomas Ford M 12 MS
son Rube Ford M 8 MS
dau Rosie Ford F 4 MS
dau Prudie Ford F 1 MS
