Shine Shoes, Wash Cars, Yard Work, House/Deck Painting/Staining. If he's good on a computer then sell family photobook creation, birthday party websites/pictures, How about DJ at a party? Baby Sitting?
Recycle. I used to make a fair amount of money just recycling the cans and bottles at my house. Babysitting is also a really good way to make money quick though he might be to young for most parents to be comfortable with. Yard work in the neighborhood is a good way.