Well, I logged on and read about the contents of the 2 caches listed in Sunset park. One is full of Scooby-Doo stuff. The other one (#1) doesn't really describe this one too well. I can't read the bottom line of the note, but my forensic expert wife has determined that it's not a childs handwriting for various reasons. We have concluded that it may be a geocache but listed on another geocache website. There are several. Geocaching has turned into a world wide sport. Most of the ones I have found have a "log-in" sheet in it where you write your name and date. Since this doesn't have one, makes me think it is not one.
So you have two options. You could keep it, show it to your friends as one of your most interesting finds. Or, try to replace it in the exact same place you found it in case others are trying to find it also, but if it's been some time since you found it, it may be just as well just to keep it.
The thing about these geocaches is that they are fun to hunt for and find, but there are so many now (100+ just in my zip code) that when a MDist finds one it's hard to determine if they are real or not. Most are in watertight cases like 35mm film canisters. Some are in magnetic key cases that are stashed under metal stairs or something. If you're not doing geocaches, you should look into it. It's very fun.