What are your kids doing?

So we took the kids to the park yesterday. I am wholeheartedly disgusted with the way the parents handle their children. My boy was having fun going down the slides until we had to have him stop because of a little girl who had peed her pants. I'm talking full front and back visible. She kept getting all over the equipment, for at least 15 minutes before whomever had her there even noticed. We were there at least another 30 mins and they never changed her or anything. To make things worse she was just running in and out of the street and they did not seem to care. There was also a little boy that was throwing wood chips at the kids on the merry go round (which also included one of my children). It took at least 2 mins before the father noticed. Who was sitting so far away that the kid (looked between 2-3 ish) could have ran off or did anything before he got to the boy, even at a dead sprint. He didn't even say anything to the boy about what he was doing. I am reasonably new to the whole parenting thing, I've been taking care of my four year old stepson since he was two and my now one year old baby. I don't understand how these parents can just leave there 4 and under children unattended in a large busy park AND not pay hardly any attention to them. Mind you, where I live is reasonably safe, but that does not mean we are immune to abduction or violence. I do have moments of distraction, but I stay within A few yards at most and never let the kids wander out of the play area without me. I just don't understand how neglectful these parent come off as. I don't presume to judge them beyond the park, they could be amazing parents elsewhere. I think that they need to pay better attention to their children. Just because there are plenty of children for yours to play with, it does not mean you can "set it and forget it".