I would suspect teething to be the culprit, or possibly just experimenting with the action/reaction of biting.
Not really something to terminate over, IMO.
When a biter bites, or even TRIES to bite, I scoop up the victim and give her lots and lots of snuggles and hugs. The FIRST thing I say to anyone is to the biter and it's a VERY severe, "NO BITING. BITING HURTS." And then I turn my back. I walk away. I ignore biter while very obviously comforting the victim.
I shadow the biter pretty closely (not "in a bubble" but closely). If my attention isn't on biter (surreptitiously of course), then biter is attached to me one way or another. Every time biter goes in to bite, my hand goes between the mouth and the victim. I have gotten adept and doing it in such a way that if anything get's bitten it's the biters own lip
. "NO BITING. BITING HURTS."
Repeated too frequently in one short span of time, biter might get thirty seconds to a minute of solitude behind a gate, or a dose of Motrin if you suspect teething to be the culprit. <--I don't usually dose for teething but when it's a biter I'll try.
I've had several biters and have kept them each through the biting phase. Eventually we come through on the other side with the child in a stable care situation and no one the worse for wear.
If you were a family and these children were all yours you wouldn't kick one out of the family for biting, would you?