am i in the wrong?

So this week i had to watch my 4 year old cousin.Well he's friends with the kids across the street (7&8) So the oldest of the brothers and my cousin started playing wiffle ball.The youngest brother goes to his house and gets a wiffle ball and plastic bat.The two of the brothers start playing wiffle ball in my front yard (not really my yard i'm only 14) The front yard isn't that big and they we'rent playing with my cousin.So i told them to leave.Am i in the wrong? (edit) my cousing had his own wiffle ball and bat they where playing with that then the brother got his wiffle ball and bat