The Nazis locked up gays, remember.
The Nazis' targeted many others because of "racial inferiority" including; Gypsies, the handicapped, Slavic people, homosexuals, Jehovah's Witnesses, and so many others that it added up to 5,000,000 without the Jews included. The Holocaust just wasn't the annihilation of the Jews, it was much, much more.
Many children experienced something most people can't understand. They were killed just as much as adults were.