Lying in prone (aka on your tummy) and propping up on your elbows to play—even to play electronics!—is important work. It strengthens the muscles in your core. It strengthens and stabilizes the joints that are propping up—the elbows, the shoulders.
Even when I get tired or unfocused at work, I’ve been known to put what I’m working on down on the floor and lay down and begin writing on paper instead of typing on my computer!
Strength and stability in your core muscles and in the joints of the arm all contribute to “school skills” that you may not have thought of before—like the ability to sit up straight and still for a long time in your chair, and the ability to stabilize your arm to produce good handwriting with the smaller joints (like the wrist and fingertips).
So whether your child is lying down looking at a book or playing on a tablet, or crawling around on all 4s pretending to be a kitty or a baby for the 683rd time (🙋🏽 hello have you been looking at my house and kids?), they are still working on valuable skills. There’s no “shortcut” to strengthening work like this, it just happens over time and with repetition!