Autistic children frequently have sensory processing differences, which can be stressful or even painful. Applying deep pressure causes muscles to relax.  Try wrapping your child snugly in a blanket or lay several blankets across them. The weight of the blankets will create soothing pressure, but be sure not to cover their face to prevent interfering with breathing. You can order or create tools designed to provide deep pressure online. Weighted blankets, toys, vests, and lap pads are all possibilities. Massage is a good way for you to interact with your child, while applying deep pressure, which may strengthen the parent-child relationship. Position the child between your legs. Cup your hands on the child’s shoulders and apply pressure. Then, move your hands slowly over their arms and shoulders. If you do not feel comfortable, consider asking a massage therapist for tips. Or, ask someone you know who gives really good back rubs. A pillow press is done by positioning the child on a soft surface such as a pillow or a couch cushion. Let the child lie or sit down, then use a second pillow or cushion to apply deep pressure to the torso, arms and legs in a slow pulsating manner.  Never cover the child's face to prevent accidental suffocation.

Summary:
Apply deep pressure. Give your child a deep pressure massage. Try a pillow press.