Was it just one time and stink a lot worse than the others? It might be a cecal poop which they do several times a day, but when you're standing there, it's pretty bad. Regardless, just in case, I'd give mine some probiotics in their water. They make several brands of powders, and ours is Hydro Hen. I'd give that to them solely as a water source every other day for about a week. That should help if they're having digestion issues.
Are they just getting chick crumbles thus far? Just checking as usually I wait until they are about a month old before I introduce anything else, which is some scrambled eggs, but also give them a little side dish of grit then too.