I have quite often heard (and even used) the idea that quantum fluctuations are a way to explain the whole "something from nothing" intuitive leap. I am about to give a talk at a local school on cosmology, and I just want to make sure that I don't misstate anything. As a layperson type of explanation, would this pass the "close enough to what theory actually states" test?
I don't think there has been much actual real research in the idea that quantum fluctuations can create the big bang. I see it more as a philosophical/theological argument than anything else. There is no "real" way to describe quantum fluctuations in non-existant space-time.
I would advise just keeping your discussion to post - big bang, as otherwise you will be either getting into highly speculative to pseudo-science territory. If some student asks, you can say something like "that is really the next big question, which maybe one of you will figure out over the next few decades!"
You can also of course mentions string theory has the whole colliding branes in the mutliverse, although that of course leads to the question "what created the multiverse?"
When explaining anything with physics, try to avoid questions that have no logical positivist meaning. The question "why is there something rather than nothing", much like "does a typical neutron prefer Chopin or Bach?" is meaningless, there is no objective way to answer it, because there is no observable consequence of any answer. The only question that science answers are those for which the answer has some observable consequence.