Going through some old boxes, I found our 21-year-old son's first iPad, iPod touch, and iPhone. We powered them up and each one was a time capsule at different ages. It had old Minecraft and Terraria worlds he played with friends, texts/photos/videos, games long since removed from the App Store.
He started up FTL and found himself in the middle of a terrible save state he ragequit over ten years ago. In Terraria, he saw gravestones marking how/where an old school friend he hasn't seen IRL in years had died repeatedly. Fun stuff!
If you have the luxury of not cashing in your kids' old devices when upgrading, consider powering them down, labeling it with info about what's on it, and storing it in a cool dry place for a decade or two. I promise it'll be more valuable to them than the current trade-in value when they're grown.
@andybaio Reminds me of the kid who booted up his old Xbox and found his deceased dad's racing game with high score still intact, and played against his dad's ghost car.