They are babies and you have to teach them how to play nice. It will take a lot of work in the beginning but it will get easier. Remind them to use "gentle hands", "play nice", "no hitting" etc. Say this while you correct the behaviour, so if they took a toy I would say "so and so has this right now" and give it back to that child. A child doesn't just know this stuff so you have to teach them and show them the right way to play.

Good Luck!!