"Has your toddler started hurting other children? It's not surprising — many toddlers act out in this way. The good news is that he doesn't mean to inflict pain on his playmates. When he pulls another child's hair, he's either fascinated by the reaction it provokes or copying an older sibling's behavior. Making another child yell or cry seems like great fun at this age.
Experts call this phenomenon experimenting with cause and effect — when I do X, Y happens — and it's the underlying reason for many of your most trying behavior problems now. Try not to overreact when your child's attention-getting tricks get out of hand — just gently but firmly stop the hurtful behavior and try to redirect his attention elsewhere. The more he gets a rise out of you, the more likely he is to repeat the behavior. Be sure he's getting plenty of positive attention, and you may find yourself getting a break."
This was my e-mail from the Baby Center this week on my childs progress.