I don't know what the current status of the program is or what the ages are, but a friend's "gearhead" kid did a couple of summers with the Go Baby Go program. They work with adult volunteers to adapt and trick out ride-on vehicles for young kids with disabilities. Kids can even get student service hours for the program.
They might take, say, a kid's ride-on toy Jeep with an electric motor, and fix it up to match a particular child's abilities and limitations. They figure out what the child needs to drive successfully and safely, like adding hand controls or adapted steering or roll bars, then decorate it and make it look cool. So there's some problem-solving and design work, as well as the hands-on work, and they get to actually watch the kids trying out their handiwork once the car is finished.
I'm pretty sure the program in the DC area has been run through Sidwell in the past? Someone else might have more info, or you can contact the national umbrella organization for details on local programs.