I had a child start biting as well around the same age, not only was she underdeveloped in speech but after shadowing her for a few days I witnessed what motivated her to bite. She would see a toy and try to take it from a friend if they wouldn't give it up she bit.

I tried different time out methods and the one that became the most effective was setting up a playpen in a separate room and isolating her for her time outs. If they act like there time out is a walk in the park then it's not effective.

My bitter stopped biting in a month and everytime she is triggered I make her give back the toy and apologize. Her bites were pretty bad she even bit another child on the eye.

I got the same from the parents that she didn't show this behavior at home but being an only child who is she going to bite her Mom? Not likely.

It's a hard one if the child is breaking skin especially if your own are being victimized. Do you think be is doing it out of jealousy? He may see the special bond that you have and feel left out. It's tough missing his own Mom all day. Maybe he needs a few extra cuddles, I always give each of my daycare kids some special one on one time. Hugs really could be all her needs.