I think you’re doing the right thing by trying to act the Christian way and being patient, understanding, tolerant, etc. But there is a limit to everything as well, and your kids’ well being is obviously an important factor to each mom out there.
If I were in your shoes, I would go ahead and talk to that little girl’s mom (the one with DS) and explain the situation to her. Yes, her mom needs a break (who wouldn’t in her place??), but it’s also her responsibility to discipline her kids and insure a safe play athmosphere exists not only for her child, but for others as well.
That little girl needs to learn how to safely play with her buddies, and it might take her more time to learn ‘how’, but the sooner she starts, the sooner she will understand. And the best person to teach her this, is her mom.
My opinion anyway Good luck.