Correct, and not only them but also certain others who weren't perfectly healthy. In Germany parents who were NSDAP party members brought their kids in voluntarily.

For more details look up Tiergartenstraße 4 or Aktion T4, but be aware that the details are ugly.

Too late to edit and also only tangentially related but I think it is worth mentioning that Nazis also tried to get rid of Jehovas Witnesses, Gypsies and probably a number of others as well.