HELP!....NEIGHBOR PROBLEMS.

So today, I had just gotten home from picking Audrey and her friend Brooklyn up. They were playing in the backyard and our neighbors, Isabella and Diego came out to play. They are five year old twins. I looked out a little later and noticed that Audrey and Isabella were leaving Brooklyn out. I decided to have Audrey and Brooklyn come in and go play upstairs. They did, and I went up to turn a movie on for Alex. While I was upstairs, I heard someone coming up the stairs. I turned to see Isabella and Diego. They had just walked in our house! I said, "Hey, what are you guys doing?" They said, "Our mom said we could come over." I said, "Oh, really?" They proceeded to walk into the play room and start playing. I have to admit, I really didn't know what to do. Somehow, I told them they had to leave and that maybe they could come back later. They just kept saying, "Our mom said we could". What am I supposed to say to that?

They are nice enough kids, but they have some strange habits. For instance, I've seen both of them going to the bathroom outside a couple of different times. They just pull their pants down and go wherever they are, who knows how many times they have gone in my yard! Another day, Audrey came in with a can of Coke they had given her to drink. It was about 3/4 the way gone! They had also been outside watching "The Simpson's Movie" on a portable DVD player. I thought that was a little weird. My four year old, "The Simpson's Movie", and a Coke? Are you kidding me?

They are constantly in my yard swinging on our swingset, peering in our back door, leaving their garbage, playing in my dirt, leaving their toys in our yard, taking my kids' toys to their yard, and now, coming in my house! I know we just need to get a fence, but the other day I was talking to their Dad about it. He said he really isn't in a hurry to get a fence because of how much fun the kids have together. He said he is afraid that if we get a fence, they won't see each other anymore. Audrey really likes to play with them and I admit, it is nice for me to be able to send her out to play sometimes. I just don't want her picking up on some of their strange habits! That sounds so terrible, I know. She just seems to get a real attitude after she has been around them. I had to yell at them today because I had asked them not to throw dirt on the patio, and five minutes later I look out and they were throwing dirt on the patio. I was so mad! I'm sure they think I'm a witch, but enough is enough! I guess I need to sit them down and set some rules or something, because apparently they don't have any at their house. It's getting to the point where I don't want Audrey to play with them. It is hard though because everytime she sees them in our yard, which is a lot, she wants to go out. I feel bad keeping her from playing, but I honestly would prefer she didn't play with them. What should I do? Am I overreacting?