Advice...

I live in an rv park, and I live on the very end of almost a block of RVs. I'm at the end where you can't see my yard from the other end. These 2 kids come over to play with my 5yo and idk their ages but they're a yr or 2 older than mine. And I feel like I'm babysitting or responsible for them while their down here. I see no parents ever checking on their kids ever. Is it right to feel like I should post a note (because I dont know where they belong) and ask for some. What if they get hurt while here? Is that my fault. I don't know what to do. But I feel like a babysitter. They were here for 3 hours yesterday. And not in my home just out in my yard. Playing with my child's things.