A couple of years ago, when my son had just learned to ride his bike (he was 6 or 7), he was riding on the street in front of our house. I had gone in the back yard to do something, my wife was watching him and watering the garden out front. Suddenly I heard the sound no parent wants to hear, a car screeching to a halt and a loud bang and the bike and car made contact. I've never run so fast.
Turns out he bashed into the left front of the car. His bike and helmet took the brunt of the force and he was OK, but I know exactly how you feel. Good he's ok. Give him a hug and help him get through the emotional trauma as well.