which is why you unplug it before working on it and make a BIG point to the kid of both hazards, and how essential it is to remove power before working on something, AND to do test runs in a safer area like outside, etc.
>>the last thing i want my kid to think in that situation is that it is okay for them to put their hands in the toaster
I'd say that you don't want them putting their hands in WHILE IT IS POWERED or HOT. Important distinction, and best started early and often. They'll see it sometime, better to have them have a context so they can tell the difference between doing the same thing when it is smart (powered down and repairing), vs Darwin Award candidate level stupid (when powered); then they can evaluate other's actions and draw the right conclusions.