...or just leave grandparents on the previous version of Stable until they get a new computer. Honestly not a huge fan of upgrading software at all, if I'm the one supporting the machines.

Just depends on if that's something grandparents/kids can/want to afford.

Personally, If the hardware is working great, seems like a waste of money replacing it, just to upgrade software. Especially with Debian oldstable -> Debian stable where it's usually quite easy and painless.