Are there any risks if my 20-month-old bites or is bitten by another child?
That depends partly on where a child is bitten and how much tissue is penetrated. The most common sites are the hand and arm, although I have had patients bitten on the cheek and even the chest (how that happened I do not know). A punch in the mouth is the same as a bite when the punched victim's teeth break the skin on the puncher's hand. The immediate problem is infection. Bites on the hand or around the head and neck are particularly prone to infection and may need preventive antibiotics, but only if skin is broken.
Parents worry that hepatitis B or HIV might be transmitted through the bite of an infected child, but the chances of that are rare. Because most children's teeth are small (though sharp), and because children's jaws can exert only limited force, the odds of disease transmission are slim to none. If your child has had all of his immunizations, he should be immune to hepatitis B. If the biting child is a known carrier of HIV, consult your pediatrician about whether you need to start preventive treatment, but the chance of the victim of a child's bite contracting AIDS is so minuscule as to be virtually zero.