For the love of Physics--or fashion?

I'm telling this story I suppose to show a few of my internal (but never stated) thought processes. I'm open to feedback--really.

Here's what happened: The children and I went to Clay Township park. A very nice place, fun to play at, and the children stay somewhat contained. There is a roller slide (see photo)at this park. Personally, I think it hurts to go down these. I've tried a few, and it's never pleasant. Perhaps my weight on the rollers changes the fun factor...or else our children are all a little loony. I wonder if the person who invented the slide actually went down it, or just thought it was a great idea. Sorry, tangent...back to what happened.

Zac had brought a shovel from our sandbox, and was putting the playground "dirt" (I would say it's more of a mulch, but anyhow...) on the slide, then going up the ladder, coming down, and noticing that the dirt would fall through the slats between the rollers before he got to it. Chayce wanted in on the race, and would go down as well laughing as the dirt disappeared. Quite the fun physics experiment, don't you think? Then, Zac started putting larger piles of dirt at the bottom, and running on the rollers, like a treadmill, to see how quickly he could get the pile to disappear. (No problems yet, right?)

Other children started joining in. What kid doesn't love a pile of dirt? AND considering the lack of science and mathematical education in the United States, I considered my children were doing a good deed by explaining this process to the cute little pre-schoolers who would listen. That all changed when another family showed up at the park. The children of this family saw the group of kids, and the enjoyment, and came running. They immediately began participating in the dirt displacement experiment, this too, was a good thing. The bad thing was when the mother of these children figured out what the kids were up to. She was very upset that her daughter's clothes might get dirty (stained, she said, but I've never had the dirt from Clay Park ruin an outfit, even using the cheapest detergent--plus, we only send our kids to the park in clothes purchased for under a dollar at a yard sale. If they are wearing Ralph Lauren, it's because someone was brilliant enough to pay full price and sell it to me from their garage). The dirt was obviously falling from the slide before the children got to it (meaning the slide wasn't any dirtier after the pile fell through than it was when we arrived at the park--clean playground equiptment? Never heard of it.).
Nevertheless, when she loudly protested, I asked the children to please make sure there was no dirt on the rollers when it was her daughter's turn to go down, but that they could all resume on their own turns. She tried to coax her daughter to swing (yes, let's go sit on a dirty, black, plastic swing that we all know leaves marks--with a chain that's been in the rain...rust anyone?), but the daughter really wanted to stay and play with the others.

Now tell me, was I wrong in not completely stopping the experiment?