Nothing upsets day care personnel more than biting. It has always been upsetting, as no worker wants to send a child home with teeth marks on the arm. But the concern intensified at the dawn of the AIDS era. Nothing frightened parents more than the thought that their child might be bitten by a child positive for the virus. On that score, much reassurance can be offered: the only child in danger in that scenario is the biter. In such a case, if a bite that drew blood occurred, the biting child might be endangered should the bitten child be positive for the virus.
But disease transmission aside, biting of one child by another is behavior that cannot be permitted. It sounds to me as though both your sitter and you are doing the right thing. In the first place, you both do the same thing. In the second place, isolation of the biting child is clearly the way to handle the situation. It sounds as though your son knows what he is being isolated for (he says he is sorry). It may be necessary to keep him away from other children for slightly longer periods. Exclusion from the group should be handled firmly and reinforced verbally: “Zach, I cannot let you bite one of the other children. You’re going to have to stay in here until I say you may come out.” (Don’t mention a time length; it won’t mean anything to a toddler.)
Finally, let me suggest that prevention works even better than time-out. A young child never bites until quite a bit of tension and/or frustration has built up. Watch for the signs and quickly move him away from the scene of the tension.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.