In the 90s, there was a sci fi book in my elementary school library about this very subject. I swore it was by William Shatner (it wasn't), and I had the name slightly wrong, so I hadn't been able to find it again until tonight.

https://en.wikipedia.org/wiki/The_Boy_Who_Reversed_Himself

This book covers all sorts of situations about objects in fewer and additional dimensions.

They might discover there are other previously invisible 2D worlds (i.e. planes) in existence right next to theirs ;)