Safety for Children at a campground

We were camping here in Washington when my grandchildren were little. I noticed this young man staring at the boys but I just kind of kept my eye on him, thinking it might be my own imagination. That evening my 8 year old grandson walked to the bathroom and as always I walked with him and stood outside. Suddenly I hear GRANDMA and I ran in. This same guy had his pants down and was holding my grandson by the arm.
The ranger told me that someone else had complained about this guy but he took off and we never saw him again. If I had been DAD or GRANDPA the guy would have been dead