Raising Relatives and non-Relatives

As I mentioned a month ago, my wife and I are in the process of adopting twin boys, so I've wondered a little bit about other adopted children in my genealogy database, and how easy it is when looking at census records to confuse parent-child relationships.

One instance is the Denyer family in 1870. 

Samuel and Zerelda (Singleton) Denyer - Children: Amanda, Robert, Albert and Ida
Ebenezer and Sarah (Hartley) Denyer - Children: William and Margaret

Samuel Denyer died in 1861, and Zerelda died in 1867, so by the time of the 1870 census, their children were orphans. It is common for a relative to assume guardianship of orphaned children, and that is what happened.

According to the 1870 census, Amanda, Robert, Albert, and Ida Denyer were living with their uncle's family - my second great grandparents Ebenezer and Sarah (Hartley) Denyer, and their two children William and Margaret.

Another instance is the Feinstein family in 1930

Harry and Dora (Servinsky) Feinstein - Children: Sidney, Adeline, Alvin, Willard, Seymour
Herman and Annie (Blatt) Feinstein - Children: Bernard, Belle, Seymour

Dora Feinstein died in 1920. Harry remarried in 1928. According to the 1930 census, he was employed as an insurance agent. However, his children were no longer living with him and his second wife. (By 1930, all but their youngest was over the age of 18, but Seymour was only 15 years old.)

In 1930 Adeline and Alvin are living with my great grandparents Herman and Annie Feinstein, and their children. Sidney Feinstein is a lodger in a hotel, and Seymour was a resident of the Jewish Orphan Home. I have been unable to find Willard in the census.

If Harry was alive and employed, why was Seymour placed in an orphan home? I'm unable to answer this question. It's possible he was placed in the home prior to his father's remarriage.

A third instance is my wife's 2nd great grandfather, Louis Pleas Gober

In the 1880 census, Louis is living with the (unrelated, to my knowledge) Kinder family in Cape Girardeau, MO. I know his father died in 1876, but I am unsure what happened to his mother.

I recently came across these statistics:

In 2010, in the State of Missouri, "there were 10,174 children in the custody of the Children’s Division."
Only "3,427 of youth placed in the foster care system live in the homes of relative and kinship providers."
I suspect the numbers in other states are similar.