Parents- How do you tell your young child they can't play with someone you disapprove of (please read details)?

There is a new family on our street. Susie (age 4) and Sam (age5) are brother and sister. Little Susie rides her bicycle up and down our street with no parent in sight. We live on a street with a cul-de-sac, so it is fairly quiet and safe, but who lets their 4 year old run around without any supervision? ughh!

I talked to another parent yesterday, and she told me to look out for little Sam. Sam was in her backyard with her son Timmy, and Sam pulled his pants down and told Timmy to “suck on it”. Sam is no longer allowed in their backyard.

Since I am a stay at home parent, my daughter will be in contact with these children almost every day this summer when she is playing outside. She already asked if she could go to Susie’s house, and I told her no because it was nice out and she needs to play outside. I know I’ll be asked again.

How do I tell her I don’t want her going to Susie’s house without telling her the real reason. You know how young children are, they repeat everything. I don’t want it getting back to Susie’s parents that I disapprove of their parenting.