safety - What is / how can I get a student-safe power supply for electronics projects?

What is / how can I get a student-safe power supply for electronics projects?

I'm looking for a student-safe power supply for solder less breadboard. I'm developing a course to teach electrical engineering to grade school students as an after-school program. I'm wrapping up the first course and I've learned a lot, including that I need to find a safer power supply. We're mostly using 9V batteries and connecting them to the breadboard via alligator clips. After lots of searching, I'm realizing that I need to turn towards the expert community for guidance. I hope that with the rise of the Makers this question will become increasingingly relevant with time as more kids get into electronics.

Inextricably linked to this question is what is the minimum power source to use. I've liked using 9V batteries since we can connect to them using alligator clips; but I worry that they are just a little too powerful. I can imagine them somehow starting a fire with them.

My #1 priority is to keep the students safe. Kids just have no concept that they can cause damage to themselves and property. When I ask "where is that smoke coming from?" I'll get a gleeful response from the student that is seeing how many batteries he could hook together and short out. I really need to limit the damage they can do. I mainly don't want anyone electrocuted or anything to catch fire. Kids will routinely attach LEDs backwards, leave them like that and then act surprised when they explode.

After safety, I want to protect the equipment. Kids will hook up a LED backwards all the time.

After protection, I want to give the kids feedback as to what is going on. A light that indicates power is on would be awesome. A light or siren or circuit break that indicated a short would be awesome too.

Battery powered supplies are slightly preferred, just to keep upfront costs low and to avoid having to run outlets to each table.

Boundaries: We are only using simple LEDs, BJT transistors, resistors and maybe a timer IC.

Similiar Questions: How to protect an electronic construction kit (a toy) from damages?

References: Course details are here: http://www.ascendly.com/classes/iee

We currently sometimes use this power supply from the Squishy Circuits Store and/or a 9V battery with alligator clips.

Epilogue

I found it tougher than expected to find a suitable wall wart, so I'm listing what I finally found for future reference. I'm about to test the following combination:

Epilogue 2

A year-plus in, I've decided to drop the in-line power switch since it wasn't obvious when it was 'on' vs. 'off'. I'm instead relying upon the students to unplug the rat-tail from the supply, which is quick and easy. Also, since I'm primarily using this for a squishy-dough project, I'm experimenting with with using two button batteries instead of a wall power.