We have had a very similar situation with a little girl in our neighborhood. She is 4 and my daughter is 5. She acts rudely toward our 2 year old son, refusing to share with him or telling him to go away. I have noticed she acts rudely to us regardless if her mom and dad are present or not. Lately, I have told her, (we will call her Mary), "Mary, we do not treat our friends ugly, and if you want to play at our house, you must obey our rules." It did take a couple of times of getting scolded at our house before she would come over and play nicely with only gentle reminders required. Consequently, we have not seen very much of her lately. I have explained to my daughter how unpleasant and rude she is, and if mommy had a friend like that, I would not want to hang out with them. She had stopped asking to play with her, but is polite if we see her in the neighborhood. I think that if my 5 year old can understand, your children are of the age where they would understand as well. If all else fails, be "unavailable" to playdates with them.