Child having a bad influence on my own

Not really sure what the course of action is here.I have a 9 year old daughter. There is a girl a few doors down that is the same age albeit a few months younger. It came out recently that this child has told my daughter what sex is, as well as periods, how babies are made, rape, strippers...the list goes on. So of course I am shocked by this, mostly because I guess I was naive to think I would be the first one to explain these things to her, and of course given her age, I was planning on talking about menstruation pretty quick here. So I sit her down and we have a very long discussion about facts, what she was told vs what the truth is. I don't want her playing with this child anymore and I make that known, but we live in a block of 4 town homes and live on opposite end units. They all play outside (and I'm pro play outside). I should also say my 6 year old daughter is out there at times as well. Eventually they start playing together again because of proximity, so every single day I am checking in with 9 year old to see what this girl has said to her. It comes out yesterday she is still talking about sex with my daughter. I think this is weird. She has introduced my daughter to words like "d*ck". While I realize I cannot prevent her from knowing everything, she is 9, and we go to great lengths to not expose her to age inappropriate things. We don't watch adult programming in front of her, we don't have cable, she doesn't have access to adult concepts period. I was about 10 or 11 when I was exposed to porn for the first time because my older brother would make me be the lookout while he watched it before my parents got home from work. I don't want this for my own kids. This child has one older sibling who is a 13 year old boy. Their parents leave them by themselves pretty often. I am a stay at home mom.My question is this: WTF do I do? How do I let my child play outside without adult supervision at 9 years old, which she should be able to do, when this kid is our neighbor and keeps talking about these things with my child? I have not talked to the mom or dad. I honestly don't think they would even care. They parent completely differently than I do, have no issues leaving their kids alone, and their house looks like a giant trash can. via /r/Parenting https://ift.tt/2FVrZiE