We had a really fun playdate today and he didn't want to go home. I did keep my eye on them a little more than I do with most kids just because I don't know him, but they were fine.
I would have him over again, but not right away, I am afraid that they will keep calling every day. He wanted to come over tomorrow already, but we have another playdate so I told him some other time.
I did meet a brother and a different sister and they were pretty nice, social and talkative. They were both in high school and were home doing laundry and cleaning because school was closed this week. The mom was out looking at a car, so maybe next time we could go to a park!
Thanks for the advice everyone!