If you're interested in focusing on Python, PyCharm is phenomenal. But as others have hinted at, an IDE is usually overkill for non-.NET development at the introductory level. Obviously don't bother with vim or emacs... the added overhead is no where near worth it for teaching, and I use nothing but vim professionally.
Sublime or Jupyter would be a very fun and simple environment. Jupyter for teaching the basics, Sublime for general-purpose projects after that.
Ultimately, the editor is so, so, so very far down the list of things that will make an introductory course work, don't overthink it. Focus your energy on getting them setup with an environment that works (installing the required dependencies and executing packages that depend on them) and coming up with projects that are interesting yet accessible. You're at an advantage with OSX, less to wrestle with than Windows and more familiar than Linux to the majority. Ruby treats OSX as 110% first-class in tutorials, setup, and dependency management, but the syntax is funkier.
The really tough thing is finding a curriculum that appeals to kids who aren't in it just for the code/intellectual elitism. I think ideally you want something with visual feedback that affords lots of opportunities to tinker and tweak, but that also serves some kind of entertaining purpose. It's more or less an unsolved problem -- is there really anything that will interest a majority?
If you're interested in teaching younger kids, I would strongly urge you to look into Scratch. It simply cannot be beat for introducing young kids to programming, and is not far from a good starting point for people knew to programming at any age really.