Autism as a condition has not been widely recognized in the early 1940s, although the first research has been made by several psychiatrists starting in 1910s and followed by people like Hans Asperger from Vienna University in late 1930s and Leo Kanner from John Hopkins Hospital in USA in the early 1940s. These was, however, only pioneer research in an early stage of development and encompassing very small samples, and thus during the implementation of the eugenic practices in the Third Reich autism was largely classified as a form of schizophrenia due to internal withdrawal and diminished ability to interact with the surroundings it shares with other conditions from the schizophrenic spectrum.

Now, it is safe to say that Nazis treated autistic people much like anyone else at a time, with schizophrenic diagnosis being par of the course. The general eugenic attitude was also not that different from what has been proposed by eugenists in some other countries although after the National Socialists gained power, the psychiatric disorders were additionally stigmatized as conditions precluding a person from being a member of 'New People' for the inability to form a 'bond' with the society. What was different were the measures Germans went to since late 1930s, as they actually introduced planned euthanasia of the people hospitalized suffering from the most severe psychiatric conditions. I'm making this distinction so that you don't get an impression that the autistic people were specifically 'hunted' in any way, they simply shared the fate of all other psychiatric patients. In the case of the children patients, one of the criteria important to the authorities was the ability to get even the most simple education. This strongly suggests that children with the severe autistic symptoms (then being, of course, considered symptoms from the schizophrenic spectrum back then) were usually deemed unable to learn and could have been marked for euthanasia.

It should be noted, however, that the eugenic practices including the T4 and 14f13 Aktion, were primarily pragmatic in nature and thus focused primarily on people unable to live on their own leading productive life with some assistance (unlike large part of the invalids). You might be interested in he general background of the eugenic euthanasia in the Third Reich I briefly summarized in this thread. Thus, people committed to the psychiatric hospitals and deemed unable to live independent existence for whatever reasons, had a high chance of ending up among roughly 70.000 patients who were initially sterilized and later euthanized in the early 1940s.

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