Sharing this scooter from Razor- It was easy for my son to use at the age of 8 years old. Hopefully it works with your child also.
There are bike camps in the community to help kids with autism ride a bike with no training wheels. After some reading, I know that around day 2 they use a tandem system. Most of the bike camps are around 240.00. Here is something that you can add to your bike to help your child and it costs less than the price of a camp.
Enjoy the summer with helping your child master some balancing toys!