Click the link below to read some good advice from Dan at Necessary Roughness. He knows whereof he speaks, having an autistic child himself. Our congregation has had to work with this issue to a certain degree as well. We could probably do better.
I also think that some of the advice he gives can apply to all families, even those with children who are not autistic. Having two young children myself, and watching my wife deal with their activity and movement during services, has made me more aware of the need for all parents to receive support from others in the church.