*** don't underestimate the intelligence and savvy of 2nd graders !
they're eight, or thereabouts, and I remember what it felt like to be that age, I actually felt quite grown up (in contrast to the kindergarteners and firstgraders) -- and was trusted to go alone on a six hour Greyhound bus trip, with no chaperone/companion (from aunt's house where I was visiting, to my home)
I agree with being quite up front with them, about hazards and death and illnesses .. they've likely seen FAR more TV than I had at that age, and they will appreciate being treated like they are mature people
they may, any time now, have to deal with the death of a pet, or a parent, or a grandparent, or another relative
one more idea --- several people use closed containers of water, or other "thermal mass" to help regulate the temperature in the incubator; I would think that THIS could well keep the temperature stable during your short trip ---
of course make sure that the incubator cannot slide, scoot, fall, or get jostled, if you have to brake suddenly, or if someone rear-ends you