Nobody knows what causes autism, but it might be some mix of genetics and environment. There's a whole range of types of autism, going from severe to mild. Children who are born with autism see the world in a different way than most people do, and this causes them not to act like regular people do. Autistic children don't have very good social or communication skills. Also if they go into public places, they might hear and see and smell so many things around them that they get really scared. They can't tune out the stuff that's not important, so they feel overwhelmed. Sometimes they even bolt and run away. Which is something I have been known to do myself when I was scared.
In the U.S., one out of every 110 children has what's called an autism spectrum disorder. Boys are four times more likely to be autistic than girls. There is no cure for autism. You just have to live with it for your whole life.
Anyway, what service dogs can do for autistic kids is they can be like a bridge from the kid's private world to the world that most everybody else lives in. Dogs can help kids calm down and feel less stressed. Studies of autistic kids who have service dogs show that the kids have less anger and don't act as aggressively as they did before they got the dog.
In many cases, children are actually tethered to their dogs, and this is like having an anchor to keep them from going into their own emotional world or else running away physically. And if an autistic child does run away, the dog can track him and find him much faster than humans can.
Families are able to take their autistic kids out in public more if there is a dog for the kid to be attached to. The kid can walk with the dog and not always have to hold the hand of a parent. Also, since many people like dogs and want to ask questions about them, it gives autistic kids something to talk about with strangers, and they end up learning more social skills.
Sometimes autistic children start doing some behavior over and over again, and their service dog can nudge them and break the pattern, which makes them stop the behavior. And kids often sleep better if they have a dog to sleep with. This is important because people with autism are likely to have insomnia, and they don't get enough sleep (which is a bad thing).
Both therapy dogs and service dogs are used to help kids with autism. The difference between these two is that a therapy dog works with kids at a school or a therapist's office. A service dog is actually owned by a family and just works with one kid.
These dogs have to have lots of training, starting when they are about 8 weeks old. First they learn a bunch of basic commands and are exposed to many different people and places. Then the pups go live with a Puppy Raiser for 12 to 18 months, where they get more training and more experiences. After that, they go back to the service dog organization for advanced training.
In order to be a service dog for an autistic child, the dog has to be calm and friendly in all sorts of situations. They can't jump up on people or sniff people or growl and bark at them. Not every dog makes it all the way through the training, but the ones that do are matched with children and their families. The family has to pay for the dog, which might cost as much as $13,000. If the family doesn't have the money, they usually get it by doing a bunch of fundraising stuff.
Having a service dog is not the answer for every autistic child, but it really seems to help some of them. I don't think I would want to be a service dog because I wouldn't want to do all that training. And besides that, a lot of strangers seem very scary to me. Not to mention that I wouldn't want to be around when a kid had a temper tantrum!