I have two, count 'em two, such children. Eating out is one pleasure I would not forgo when we adopted the twins over ten years ago. I have found that other diners do not care to be involved in a social experiment and prefer that families with autistic children just stay home . . . for the next twenty years.
The onus is on us parents to make the trip successful. My tips:
Go early, so that the restaurant is not too crowded and the waitstaff are not frazzled. But not too early, when there might be a single waiter for the whole place.
Never go anywhere that requires a wait for a table.
Avoid eateries that cater to families with children. The food is awful and there are lots of children whose behavior is not a good model for yours.
Avoid places that are so quiet you can hear glasses and silverware clink, but
Avoid loud restaurants, or ones with piped-in music. It's unpleasant and over-stimulating for autistic and hyperactive children; they can't tune it out.
Order ahead. Restaurants love quick turnover for their tables. Call your order in, sit down, eat and leave.
Request a booth, if possible, off the main traffic route. I have learned the hard way not to sit too close to senior citizens, in the main area, or near the entrance. I do not relish being entertainment for the entire restaurant!
Bring engaging activities: pad and crayons, music, small toys. Play "I Spy" while you wait.
Remind children about expected behavior. Our family's rules are: "inside voice only" and "stay in your seat." If I give more than one warning for each, we have to leave.
Let other adults at the table know to decide immediately what they want, so that they can order the first time the server approaches. If someone needs "another minute, please," they will be sorry and so will your child. Also, you may never see your waiter again.
Tip the staff well.