As you may know, we recently got a puppy because we had read that dogs are good for children on the autistic spectrum.
Leo is still a puppy and has just started training with the scariest dog handler ever, but already he has bonded with our eldest son. Despite instructions from the trainer to 'ignore the dog', our eldest always has to say good morning and good night to the pup and to be quite honest, this makes him so happy I am disregarding the trainer (at the risk of being told off and made to lie down submissively at his feet..).
Our eldest takes him for a walk sometimes before school, always after it, and has already taught him to sit. Because he is very sensorily sensitive and volatile, I had imagined having a dog would provide comfort for him when his is angry with the rest of the family or feels unfairly treated (which is quite often, to his mind). To my great joy, this seems to be the case already. The dog has given him something to care about that isn't himself and this is quite amazing.
However, training is a long process and having a dog is a large and long-lasting undertaking, however beneficial it might be for the children. I have just found a site that offers Autism Assistance Dogs that might be worth considering if you have autistic children between 3 & 10 and are thinking of having a dog.
The site, at http://www.support-dogs.org.uk/AADogs.htm says, "Our Autism Assistance Dog programme is designed to improve the quality of life of families with autistic children. It is based on the principle of providing a fully trained dog to the parents and the autistic child along with the correct training and support to ensure that the dog works to the maximum of its abilities."
This kind of dog would not be not be necessary for our family, for example, as our boys are high-functioning, although our youngest has a nasty habit of walking out in front of cars. But I can see how useful one could be for more severely affected children. Disability Support dogs aren't just for autistic children, but for those with other disabilities, especially epilepsy.
Take a look at their site - it's a cause well worth supporting. Donate if you can.