Many of my friends with a child with Autism spend a one miserable Christmas after another. They go to great lengths to block off the Christmas tree and all the other decorations. I do not know about your young child with Autism, but both of my daughters with Autism Spectrum Disorders could scale anything I put between them and the tree.
They could climb with the best climbing little boy in our neighborhood. So putting things up high did not help either. I do know one family who attached the tree upside down from the ceiling one year. The ornaments then hung down from the tree. It sounds strange but was actually a beautiful tree. It also worked to keep the tree away from their child with Autism.
I have friends that have one tree for the family and another for the child with Autism. That way she can take the ornaments off and play with them. Later she can redecorate her tree with them as she pleases. They also do not put lights on her tree.
Planning for Christmas takes place at our house at the end of the last Christmas. I early on decided I did not want to spend my Christmas guarding the tree. For years and even now I am on the lookout at all the after Christmas sales. We look for ornaments that were non-breakable.
Some of what we found was soft ornaments, like miniature stuffed animals. Other ornaments we found were bells and plastic snowflakes. Still other ornaments were Styrofoam balls covered with red and green thread. We also found a lot of ornaments at our local Cracker Barrel. Some were made of wood, metal, and resin.
Any and all of these were perfect for our tree when the price was right. The ornaments were so cheap that if they got lost or damaged it was no problem. I really let my children take the ornaments off the tree and play with them. Now that they are older they are not so interested anymore. They just do not even seem interested in the tree anymore.
A really thrifty and clever person could even go to thrift store to buy small stuffed animals to make into ornaments. I have seen beautiful Christmas trees at our Junior League activities that were decorated entirely with small teddy bears or small angels. This would certainly work for a family with a child with Autism.