Have a look at both meshtastic and meshcore. You say you've already seen some meshtastic nodes, but a lot of people are moving to meshcore, and so you might have better luck there.
Also, with your node antenna up at the crest of the house roof, I would think a mile should be doable to your kid's school.
It may not work while they're in the building itself, but if they are outside, then I don't see why it wouldn't work.