My kid has spent each of the last 10 years in pods. Since he was prenatal.
Only once did he leave his seat when he shouldn't have. Just before he turned 3, in KE F.

For weeks leading up to trips, we explain what is going to happen.
When to eat, when to watch tv, when to sleep.
As long as there's a teddy bear, a blanket and a book, things have been fine.
Sitting behind a child has worked best for us.
It's easier to watch and talk to them.
I find I have to talk louder when sitting across the aisle. And no one wants that!

He's done two mini rtw's. Will do two more next year.
When possible avoid domestic red eyes.

Remember, a kid in a pod, can't kick the seat in front of them.