Yes, I'm overprotective, but I ended up giving in (see previous post). I had a couple of nice, rather lengthy phone conversations with Birthday Boy's mom and her family's values seem similar to ours.
She only allowed Birthday Boy to invite a few friends to the sleepover and he ended up with a pretty small turnout. Of the 3 other kids that attended, Son #1 knew two pretty well, plus I know the parents of one of the other guests (who is also a neighbor of the Birthday Boy's family) so I did let that influence my decision a bit.
Son #1 ended up having a great time. (Whew!)