What did they do with the kids under 10 at the concentrations camps during World War 2?

Starved them. Forced them to work as slave labour. Conducted torturous medical experiments on them. Separated them from their parents and family. Heaped verbal abuse on them. Allowed them to suffer sickness without medical care. Killed their parents, and killed them for the slightest cause, on a whim, or for no reason at all.