But now, there's evidence that having a pet can change some of that behavior.
Researchers took a look at 260 children with autism, some who were given pets, and some not. Their conclusion was that having an animal in the home can make a difference to autistic children and their families.
Take the Mandell family, who have a 5-year-old autistic son, Sam, and a 3-year-old service dog, Hagrid. Hagrid has changed the life of the Mandells and their four other boys.
"He's a different kid now," said Jennifer Mandell, Sam's mother. "We can go anywhere. It's just amazing."
Pets can make this difference for any autistic kid, says the study. Pets can calm the children and help them socialize better. To interact best with an animal in the home, kids must be at least 5 years old.
"They need that constant loving, and it's fascinating for them, something else moving, something dependent on them, something interacting with them, and it's not all verbal," said Dr. Asma Jamil Sadiq of Beth Israel Medical Center.
Autism makes it hard for Sam Mandell to go out with the family. He used to lie on the ground at the mall and refuse to move, or worse, run off in dangerous places. But now, with Sam and Hagrid tethered together?
"If Sam tries to take off, Hagrid just sits down and won't move and that gives me enough time to get Sam back," Jennifer Mandell explained.
Pets don't have to be specially trained, as Hagrid is, but there may be some advantage to a service dog. Caroline Sandler, from the Healing Autism Program, trains dogs for autistic kids.
"The dog's energy level is very low, and because the dog is handling so much of the pressure, the parents are in a better place than they used to be," Sandler said.
For the Mandells, the pressure on the family before Hagrid took a toll.
"We started fighting," Jennifer Mandell said. "I was depressed."
Sam's father Robert Mandell agreed, saying there was "tension, bickering [and] arguing" in the family, "but it was escalating."
Jennifer Mandell added, "But since we've had Hagrid, it's totally different. We're back to the way we used to be. It's not as stressful as it used to be. Everybody's happy; Sam's genuinely happy, which rubs off on all of us. He's just a happier kid."
Dr. Sadiq commented that the study was a small one, but with encouraging results. It was in the public library of science one. Service dogs take a year to train, but with more training with individual kids and their families.