I was just about the say this. We have taken our kids out to restaurants since they were in their infant carriers. They have been expected to sit still and behave, and on those occasions when they could not, we removed the child to the car while the other parent had the food boxed up and paid the bill. I do not believe in inflicting my caterwauling, rambunctious young'uns on other people.
My youngest son, Christian, is very mentally handicapped and autistic. He's much like a 1yr old in his manner. When we take him out, we always get a booth so can corral him in his seat. If he can no longer remain seated and calm, one of us gets up and takes him outside for a few laps around the parking lot. That's usually enough to change his mind and he's ready to sit down and resume his meal. Now...if an 18 year old with an IQ of 20 can learn to behave in a restaurant, SURELY those parents can figure out how to teach their boys some restaurant manners.