At conference, someone said you can buy a motor on ebay that you put on your regular bike. It will pedal for you when you don't feel like it. Search something like motor for bicycle...let us know what you come up with!!! Good luck!
I have actually been looking into electric bikes as well as electric scooters. There are several electric bikes out there. Schwinn makes some as well as other companies. They are pretty pricey though and I havn't found one small enough for my almost 7 year old (with training wheels) that we could actually afford. There are also electric motor kits available. Google electric bikes and you'll get a good idea of whats out there.