Motorcycle Wheel Repair My Son Has A Gas Powered Scooter And The Back Wheel Is Wobbly, And The Chain Keeps Falling Off. HELP!?

My son has a gas powered scooter and the back wheel is wobbly, and the chain keeps falling off. HELP!? - motorcycle wheel repair

This line was purchased as a Christmas present and, of course, I do not always provide customer service. I paid $ 300 for gas scooters and will be installed once. Needless to say, I am disappointed about 11 years and have asked numerous workshops, bicycle or motorcycle or small engine repair, and no one can help me. Any idea or suggestion? Thank you very much.