I've tried learning apps with LLMs and part of the issue is that you can't have much of a conversation early on. A conversation of "how many cats do you have?" "I have two cats" "what color are your cats", etc., isn't much different than the non-AI lessons. At the point where it would be really useful, the other options you mentioned are much better choices.
I think having a world (3d maybe, or maybe just 2d) you could talk about in a really simple way might be useful here. Imagine something like "el gato quiere la pelota roja" and you have to carry the red ball to the cat to pass to the next lesson, and there's a cat, and a dog, and capibara and various shapes; something like that...
There's probably the opportunity to have simple stories and personalities come into play too, early on, to add interest. Think about e.g. the Frog and Toad books for children learning to read.
