What was I thinking?

It was another beautiful spring day, and despite my migraine, I wanted to take the kids to the park. I think they're getting bored of our usual park which is fenced in and just big enough for lots of play. Because of that, I wanted to take them to one we haven't been to in quite sometime. Whites Park is one of the many parks in our city and it's the largest. It has a huge wooden climbing structure and it's hard to keep an eye on the kids at all times. I thought that Wes was really good at staying in one area and has been coming to find me if I call him, that we would give it a shot. Bad idea. It wasn't busy by any means, but it was brand new for Casey and he wanted to explore every nook and cranny. That made it more difficult for me to keep track of them both. Mind you, I'm not one of those mom's who sits on her butt and talks on the cell phone from the time they arrive until it's time to go. Casey was off on an adventure and I couldn't find Wesley, nor could I hear his ear piercing "eeeeeee". I called him a couple of times, and then I heard it. He burst into tears and starting nearly hysterically crying. I grabbed Casey and ran to find him. He ran towards me crying and I just scooped him up and looked him over from head to toe. I couldn't find anything wrong with him, and of course I couldn't ask. Well I did ask, but didn't get a response. We left after I got him to calm down a bit and he settled all the way on the drive home.
I have no idea of he hurt himself, if someone hurt him, or if he got scared at a kid yelling and running. That really sucks! My mother instinct tells me that I'm nuts and should have been watching him at all times, while my realist side says that you can't watch him 24/7 and he has to learn. Which side is right? He can't explain to anyone if something is wrong or worse if he gets lost. It certainly is a park where you need two sets of eyes, especially if you have small children. Needless to say, we won't be going back to that park anytime soon unless Tim and I go together. And again, I feel sorry for Casey because he was loving it.