You’re also reading a book, which is far more active than just passively watching stuff on a screen. A typical two year old has no trouble watching tv, but can’t read a book. Reading is a more cognitively taxing and attention-demanding activity, even when you’ve mastered it. Then beyond the raw reading, you have the activity of your imagination working to conjure images of what you’re reading, which is yet another layer of attention.
Reading is the best.