Get your son a Cateye TL-LD1000 for the back of his bike, and a bright light for the front. If he can see well enough to ride now, a battery powered light like the Cateye EL-500 will make the cars notice him. I've also got a white blinker for the front.
http://www.performancebike.com/shop/...tegory_ID=4320
http://www.performancebike.com/shop/...tegory_ID=4322
http://www.rei.com/product/47468138....HP_CYCLING_TOC
http://www.rei.com/product/11068458....HP_CYCLING_TOC