I have a cousin who is autistic and DH has one as well. His cousin isn't as 'severe' as mine. But one thing I noticed is the way people act. In my family we treat my cousin 'normally' very little special treatment or allowance. We sk things in the way he can respond and check things with my aunt/uncle first. However dh's family treat his cousin who is only mild very fragiley. They treat her different

Personally I would be open and honest to your daughter about this boy. That he has autism which means his thoughts are different. He is still a good boy just like you but he thinks very differently and uniquely.