I use to send my mother and husband links from youtube that explain autism in short videos, so it wasn't like info overload to them. My older kids also watched them so they could have a little understanding on there little bother specially because they had a lot of questions on why he would hit himself, or why he didnt talk or always flap his hands.
Best of luck

Processing information is a killer same goes for that one . Tell you the trouble I've had with that . As child when I had no clue what's going on until now adult with 2 kids and I still get :? But again same thing remind myself Monday not same as Tuesday nether any day like before . For me it's a good way to feel flexible even if I have supper dupper problems . Don't sugar coat tell them truth just tell them always loop hole to every problem and don't just relay on work of professional coz they wear a suit and tie and they are doctors . Your body is telling you your info in its own way x

Agree with previous answer . However also explain this is not the case all the time . If you say to someone autistic or not . An idea ok this thing called autis um means your effected sensitive to light smell environment etc the senses overload you encourage a fear or a behaviour they start to believe it's like that everyday . Explain even if this is the case . If you were exposed to same stimuli on Monday doesn't mean you have the same reaction as Tuesday :)

tell them they are over sensitive to light sound touch taste and smell and instead of tantrums experience se4nsory overload due to environment and processing information