What prompts the hitting is he bored, tired, hungry, frustated? Any cues that its going to happen, then perhaps you can distract him. Can you ignore his behaviour (to a degree anyway) and focus on the person that has been hit. He is getting attention from you for his behaviour, even if it is negative, and this for a young toddler is better than no attention at all. So ignore his behaviour as much as possible and focus on the victim ensuring they are ok, got something to play with etc etc. You must be consistent regarding your response too. Regarding the day care I would be either raising it with the day care provider, although she may not see it the same way as you unfortunately and deny her son is doing this, or find a new day care. Personally I would be looking for another, this is not a good example to be setting for your son when you are trying to get him to stop this habit. Monkey see, monkey do if you know what i mean. He is modelling his behaviour on this other kids.