Some links for this ... I have purchased some of the poly beads to try this out for my (now grown) daughter, she doesn't have autism but does have sensory issues and a lot of trouble sleeping.
My middle daughter, who is a behaviour therapist for children with autism, says these are very effective! They even have weighted belts to help calm the kids.
http://craftnectar.com/2009/09/03/ca...hted-blankets/
http://www.crapivemade.com/2010/01/w...-tutorial.html
http://www.davidsblanket.com/downloa...structions.pdf