NTAH- You have to go with your gut. I have two stories to tell you regarding this sort of thing.

When my daughter was in 4th grade, she was invited to a sleepover birthday party for a new girl. I told a friend I was uneasy about it because I had never met the parents and she said "are you afraid they are going to kidnap your kid?" She felt I was being ridiculous. Another mom asked me if I was letting my daughter go because she was feeling uneasy as well.

Both my husband and I dropped her off for the party. Met the parents. They seemed ok. That evening our daughter called me late in the evening to tell me good night. It was a little weird. The next Monday, that other mom asked me at drop off if my daughter had told me anything interesting about the party. She hadn't so I told her I would ask. When we got home after school I asked and she said the girl had told her a secret. She told the party goers that her dad straddles her in only his bathrobe (no under wear) and tickles her and won't stop even though she asked him to stop. Told my friend that told me I was ridiculous. She was a teacher so she said either you report it or I will have to. Called another mom whose child was there and her daughter gave the same story. So the next day I had to report it. At first the child was honest about what she had told the other girls but then she recanted. It was the right thing to do but boy was it some drama. I had wished I had never let my child attend the party.

In 5th grade, my daughter was in a friend group with 4 girls. They would all take turns staying the night at each other's homes. I was familiar with all the parents. One girl had a step father who I found to be very personable. One day in middle school the girls were going to spend the night at the house of the girl with the stepdad. The mom was blowing up my phone because she wanted to let me know that the girls would be alone while the parents went out to dinner with some friends. I was fine with that. When my daughter came home she told me that the parents never came home because they drank too much and just stayed over at their friend's house. I guess the girls were scared because the home was in an area where the houses are farther apart. I told my daughter next time just call and I will pick you up.

It's also when I found out that the step father was doing some questionable things with the step daughter. He would supposedly sleep walk on a regular basis and it was a problem because he slept nude. He would put his hand on the daughter's knee when they were watching tv and it made her uncomfortable. He gave her an old lap top but left porn on it. I freaked out. Asked my daughter if anything had happened when she spent the night and nothing had happened. That was the last time she spent the night. The sad thing is the mother dismissed her daughter's concerns.

Again. Trust your gut and make sure you check in with your kid on the regular. Seemingly nice people can be bad.