This will probably end up being a little long because I ramble a bit, so I apologize ahead of time.
I have a 6 year old daughter I will call N. She has gotten close to a girl in her class this year called C.
When the weather is nice and we don't have any time restricting plans, I have my kids dismissed as walkers and they come straight down to their school playground. I'm always there waiting for them, and they play with their friends for at least a couple of hours while I chat with other parent friends (and obviously keep an eye on my kids at the same time). This is how I finally got to meet C. She is a very energetic girl with a sassy goofy personality similar to N so I can easily see how they became friends. However, I quickly noticed that I never saw either of her parents around the playground. Turns out, C's mom sits in her car across the playground the entire time, always on her phone. I've only seen her get out of the vehicle once or twice when she needs to tell her girls it's time to go. I don't agree with not being nearby to keep an eye on your kids both to make sure they are behaving and playing well with other children, but also in case they get hurt or need help. But everyone parents their own way, and maybe she's not very social, so I brushed it off for the most part.
During one of our after-school-playground times, N was playing with C and I saw them run over to C's mom's car together when C had to leave. I kept an eye on N as she said goodbye. She climbed up onto the runner of the car to give C a hug in her seat, chatted for a minute with C and the mom, then all 3 of them came walking over to me. The first thing N says in a surprised/excited voice is "C and L (the younger sister) don't have any boosters or anything! They sit in the big seats!" C's mom laughs a little and says "I know, it's terrible! I really should have them in boosters!". Remember, C and N are both 6 or 7 years old, and L is 5 or 6. N says she and C want a play date some time so the mom brought me a paper with her phone number and C's name on it - not her own name - and asked for mine in return. I wrote my name and number down and thought maybe we could organize something in the future. This was probably 3ish weeks ago and neither of us have reached out to each other but N regularly asks if she can go with C when they leave the playground to get ice cream or donuts or wherever they are going. I always say no with a legitimate excuse like needing to get homework and dinner done, etc.
Last week, N came home and asked me what sexy means. I asked her where she heard that word from. She told me she heard it from C, and that C told her it means "when someone is naked and they're in the pool and they flip their hair around looking all beautiful". I told her sexy is a grown up word and not appropriate for kids, and that I'm not sure why C knows that word or what it means, but that she shouldn't at this age. The next day we were at the playground after school and I asked other parent friends if they know anything about C's parents. I am not from this area originally, I moved here with my husband about 10 years ago. However, many of the other parents I am friends with grew up in the area and know more about other families than I do. 3 different parents that I trust completely (one of which is a local police deputy, another is a nurse at the local hospital, and the other is a firefighter/EMT) all had negative things to say. They did not have much to say about the mom, but the dad is a known cocaine addict and possible heroine user. He was fired from a big-name car dealership for theft and opened up his own auto sales business in return. As one of the dad's put it, he wouldn't trust buying a golf cart from this guy, let alone a car. They also pointed out that the mom only ever wears long pants and long sleeves/cardigans no matter the weather (it can easily get into the 80s-90s with high humidity in the warmer months here), which makes them wonder if the husband is abusive and/or she is hiding track marks herself. Many of them also had not so great things to say about C's behavior. She yells at and hits her mom very hard with the mom having no reaction other than giving her what she wants or bribing her with things to distract her. She gives a lot of attitude if another parent stops their daughter and C from doing something they shouldn't be while playing together, such as climbing on top of the tunnel slide and trying to walk on it, running into the parking lot without looking both ways first, things like that.
In general, it sounds like C's parents don't do much parenting as it is and C has behavior issues because she is given free reign of what she wants and does. I also am very uncomfortable with her parents' behaviors and lifestyle. I do not want my daughter over to their house, obviously cannot trust them to take her anywhere with them such as out for ice cream as mentioned before, and I'm starting to be wary of the things C is telling and showing N when they are together at school. I know C is just a very young child and these things are not her fault, so trying to stop their friendship from growing further makes me feel guilty. I'm also fully aware that outright banning them from being friends will likely push my daughter to become closer with C as a result. All of that being said, I don't know how to broach this situation with my daughter. I can only say no to these invites and play date ideas so many times before N starts to ask me why we can never hang out with C and why she can't go to her house, etc. I know that if I'm honest and say things like "I don't trust her parents", she will take that back to C and repeat it and things might snowball. I've never had to deal with a situation like this before. A little guidance from others would be really appreciated!