Not so fun day at the park...

So yesterday I decided to take Little Dude and Little Diva to the park after picking Little Dude up from school. The park itself is literally right next door to his school, so it is always a treat for the kids when we have time after school to stop by and play for a while. Well, yesterday was one of the days...perfect weather, a ton of free time, and that was that-we were off to the park. As soon as we get there the kids run off like they have never seen a park in their entire lives-they head straight to the jungle gym. As soon I got settled into my comfy little bench, I do what I assume every parent does-I start checking out who else is at the park...what they are doing...try to figure out who is with who and so on. As I am looking around I can clearly see there are two groups of kids on either side of the park(which isn't very big) and then my kids off by themselves-thankfully. Guess what happens next? These children start having a shouting war...bantering back and forth. They are all between what appeared to be first and sixth grade. At first it was silly kid stuff. BUT then...the older kids started screaming profane words and horrible things at each other. Then the younger kids started copying them. I wanted to scream...I mean I was down right mad! How dare they speak that way, especially in a public place! I could not believe my ears. I took a quick look around and of course I am the only parent at the park that day. Ugh. I probably should have stuck around and explained to the children that they shouldn't act that way, or ask them to stop. But I was so uncomfortable I grabbed my kids as fast as I possibly could and  high tailed it out of there. After all I can not parent every child that was left unattended after school right? I did however take the time to talk to my own children about the situation, and respect for others. I still feel really bad about the whole thing. What would you have done?