I don't understand

Today we went to the sprinklers in CF to play outside, since we've been trapped in the house for way to many days due to the heat and hot weather. When we got there I noticed about five or six kids there, alone, with the oldest being about 13-14 years old, and the youngest probably Gracie's age. No adults. I just don't understand how a parent can allow someone that young to be responsible for that many kids at one time. Of course, I was most concerned about the youngest boy, because he had almost zero supervision. He had a regular diaper on, so soaked from all the water that it was basically falling off of him. At one point the babysitter girl asked me if I had another little swimmer for him to wear, because they didn't have any. I didn't bring any extra with me, but I wished that I had. I know he had to be uncomfortable wearing that big ol' wet diaper, but toddler that young don't know the difference I guess.
Being a Mom, and watching these kids run around basically unsupervised, made me sick to my stomach. The sprinklers are out in the open, on the corner of a busy street, with concrete underneath them. There are fountains that surround the one side, that light up at night, and big signs warning you to stay out of the fountains because of the risk of electrical shock. These kids were playing in the fountains when we got there. What if something had happened to one of them? Who would help?
I know I overthink things alot, but when it comes to kids stuff like this really bothers me. I just hope that they are okay and no one was injured today after we left.