If you interact with babies, you'll notice that they are looking at you with an astonished intensity. That's because every neuron in their brain is trying to understand "What is going on!?"

Humans are copy-machines. We copy each other. Toddlers and infants especially so. They don't learn by just hearing voices, they need to see how these sounds are made by a real human being with a real voice-box and real lips and real tongue, in which context they are used.

Have you ever noticed gesturing while talking to someone on the phone? That's because we constantly try to enrich the words we are making with more context.

All that is missing if toddlers are just looking at a screen. It's devastating for learning.