You could try putting the kids in another room anytime they are too rough with the animals, and tell them they can't be around the animals unless they can be gentle. Tell them they are welcome to come back out when they are ready to be nice to the animals, but if they continue the same behaviour, just keep putting them back into the other room. At the age of 2 being separated from the "fun and action" (i.e. being away from other people) has the most impact, I find.