Introduce firm pressure. Each day and evening shake your child's hand with a firm grip to slowly help the child get used to this sensation. When the child is used to it, vary your handshake with light and firm pressure.
Regulate your child's exposure to sound. For example, if your child reacts badly to high-pitched noises, keep him away from car alarms, sirens and blasting car radios. Gradually, over a few weeks to a month, expose your child to different types and pitches of sound, by allowing your child to hear these different pitches for just a minute or so. Then gradually let the time increase as your child adapts and the noises become less jarring.
Regulate your child's exposure to light. If your child finds bright lights disruptive, keep dim lights in your house and in their room. Over time, let your child come into increased contact with bright lights in malls, museums and other public places. This exercise can be done for smell and taste as well.
Play modulation and regulation games. Show the child how to react with his world in degrees. For example, if your child is running around the house super-fast, you can ask him if he can run simply fast, and then slightly fast, and then walk quickly to walking slowly. Show your child that they control the level of intensity.
Repeat the previous exercise with sound. Ask your child if they can make soft noises, then louder ones, then the loudest noise of all. Ideally, the child learns to adapt gradually. This exercise can be done for smell and taste as well.
Introduce your child to "heavy work" activities. Such activities provide the neurological input that under-reactive children crave as they combine the tactile with the physical. The possibilities for heavy work activities are endless and an under-reactive child needs them daily: pushing a shopping cart, carrying groceries or a diaper bag, swinging on a jungle gym, raking leaves, shoveling snow and cooking activities that involve stirring, pressing or kneading.