By ADA regulations, it depends upon the direction the wheelchair is approaching the switch. If the switch is accessed from the front of the wheelchair, the maximum height to the swicth lever (not the bottom) is 48". If the switch is accessed from the side of the wheelchair, the maximum height is 54". These dimensions are mainly for adult use and should be reduced for children. Since it is your home you can place the switches anywhere you want. Ask your son to point out what feels good to him. In my house I placed two switches, one above the other. The top was at standard height so that other users would not be confused searching for the switch. The second was placed at 32" so my children could easily access it. I used two 3-way switches (as I would use if the switches were located at opposite ends of a room). The wiring is somewhat more confusing but is not hard to do. You will find a diagram for this arrangement in any book on wiring. Instead of 2-#12 w/ ground you use 3-#12 w/ ground. This is a neat solution that makes everyone happy.