I'm not suggesting that you give the kid a phone and leave them unattended. But you, as the parent, could totally hold your phone up in AR mode so you both can see what the plane is, and where it's going. Maybe make it a little game. Guess where it's coming from, where it's going to, what kind of plane - then see the answers.

If I build and give the kid a display so they can simply stare at it all day without any human interaction... how is that better than the AR on parents phone? It's not, it's worse. (Note, I'm not saying that's what the author actually did, just proposing an option)

The technology here is not the problem. Be in AR or CRT. The problem is how we use it and how we teach our kids to use it.