Children usually bite other children when they're unable to communicate their feelings. Some children bite due to behavioural issues.
Our four year old is in junior kindergarten and there's a girl in her class that apparently bites other children often because she has behavioural issues. Our daughter likes to play with this little girl and has been bitten by her more than once. The teacher can't keep them apart, but she does keep an eye on the little girl and takes appropriate action. One day her teacher approached me and advised that our daughter bit a child. I was shocked because she never does that. She was obviously copying the little girls' behaviour. I talked to her teacher and she said when the other little girl bites she gets sent to the office and she thinks our daughter did it to get the same kind of attention. My husband and I talked to our daughter and told her that biting is not nice and she should always use her words. We explained to her that when the other little girl goes to the office it's because she's in trouble and biting is not acceptable. I'm happy to say that she hasn't bitten anybody ever since.
If your child is biting other children talk to him/her to find out what is causing their frustration. It's important to understand the reason behind the biting so it can be stopped. If your child is being bitten by another child, make sure they get medical attention to check the severity of the bite. Talk to the teacher to find out why the child might be biting and find out what precautions they are taking to prevent it from happening again.