It's probally just a common American Toad, they are found all over the midwest and actually make great little pets. The kids should enjoy it, just make sure they wash their hands after touching it as they do produce toxins, and will "pee" signifantly as a defensive action when handled. Those are the only two major negatives and might make it a "look - don't touch" animal , especially for pre-schoolers.
They do burrow so it would be good to replace the mat with some coco-coco substrate (found in a brown block) at pet stores. One or two inches of it should do it, and don't be worried if it fully burrows under the substrate, it's what they do. They won't climb so no need for the climb log, but the hidey hole and the water dish is a must.They are nocturnal animals, so unless you dig it out it's common for it to stay hidden during the day. It was probally drawn to your back porch light looking for bugs.
Depending how small it is they do well on earth worms, red worms, crickets, meal worms, pill bugs. They will eat until you stop feeding them so just watch for over feeding, good rule of thumb though - if it looks fat, it's happy. Toads shouldn't look skinny, it's hip bones shouldn't stick out. Thick limbs and clear eyes are a good indication of a healthy toad. If it's a young toad (smaller then a half-dollar) get some calcium dust from a petstore and dust a few worms or crickets with it every week, to help promote healthy bone growth. They grow fast.
No need for any heating pad or heat lamp, they do just fine at room tempatures, even when the heat might be turned off at night at your school. Don't worry about it feeling cold, it's quite natural for them being cold-blooded out in the midwest, especially on our cold spring nights. You'll actually have to feed it less and from my experience they live longer.
The females get quite large, sometimes as big as a woman's balled fist so it might out grow out of 10 gallon tank pretty quick, my suggestion would be a 20 gallon which are VERY cheap at most petstores and you can even get some super cheap or free on www.craigslist.org
Good luck! And if you have any more questions I'll be happy to fill you in on American Toads more ... they are about the easiest, hardiest little toad/frog to care for.
The kids will probally enjoy bringing in earth worms and pill bugs from the playground after little rain showers to feed it.That is.. if you want them touching bugs, hah.