We had the same issue w/ my son. When he was around 12 mos of age we placed him in a daycare. One day after he woke up from his nap, there was another baby that had his hand hanging out from the crib and our boy just went up and took a bite out of the baby's finger. From that point forward, he learned about time out in the corner. Now, he was only 12 mos old so timeout only lasted 1 min and he did not face the corner. We also talked about being nice and what nice was. We also related it to rubbing the other persons head gently. This has helped greatly since he's now 2 and we're working on sharing and reinforcing being nice...
