Zero tolerance is how I deal with any kind of problem like this. I stop problems before they escalalate and I use timeouts, discussions about taking turns or whatever the problem, plus I have a little daycare ditty. Daycare Cool Rules: No hitting, no pushing, no throwing toys, yes friends, yes hugs, good girls and boys. It sounds corny but I make them repeat it and remember that we are always nice to one another.
I'm not saying that we've never had issues, we have of course, but I'm on these little guys like a wet blanket when the slightest problem occurs and in over 5 years I've never had any really big issues. If you stop it right away it never becomes out of control. Easier said than done, it's exhausting to make it work and always be on duty, but it does work.