Are you aware of any research- or can you tell from your own children, after how long they tune out and stop learning. Let’s say a 18mo wants to watch a dvd for quite a long time…20, 30 minutes… will she still be receptive or are only the first minutes crucial? What about LR? Flashcards etc…
In my experience my daughter is interested in material that is new. She can watch a 30 minute DVD straight through, but once she has seen it a few times then she will only watch a couple minutes at a time. I take her being bored of something as a sign that she knows it and I move onto something else. I don’t assume that because she is not interested that she is no longer learning, but rather that she already knows it.
My daughter also has an increased attention span now, but if she watches something worth remembering (like chinese characters, or new signs…) is she likely to remember the signs after x many minutes, or is it better to break a dvd into small showing sessions?