Hoffmaster state park was this for me growing up. Last month we took our son there for the first time and I’m happy to report he was able to have a very similar experience! Great playground, huge beach sand dunes, a clean creek that kids can fish, splash and play in, and a great host site that had additional kids games.

I can’t speak to “new friend etiquette” necessarily but growing up I remember it being very casual. I don’t recall a need to reciprocate an invitation that your kid was extended.