A knocked-out baby tooth looks worse than it actually is. While it can't be reimplanted like permanent teeth can, it's unlikely that your child's future teeth will be affected. Ditto for his speech development. He may have a lisp for a little while, that's all.
If it looks as though your child has injured more than just his tooth, go to an emergency room, where a doctor can check his face, mouth, and gums. Otherwise:
1. Apply direct pressure to the gum with a clean washcloth or rolled-up piece of gauze. If he's old enough to understand, have him bite down on it gently.
2. Find the missing tooth and put it in a small plastic bag. Even though it can't be reinserted, your dentist may still want to see it.
3. Call your dentist. Depending on the injury, he may simply advise you to put your child on a soft diet for the next 48 to 72 hours. He may also suggest that you bring your child in for an x ray. This will help him determine whether there's been damage to the nerve or to a secondary tooth, or whether there are missing tooth fragments, which can cause adult teeth to come in crooked. If a baby molar gets knocked out, the dentist may put in spacers to guide in future teeth.