When I tell my kids the story of The Tempest, I usually spin it so that Ariel is a playmate of Miranda's, playing hide and seek (tricky with someone who can turn invisible), turning into various animals, and generally hiding from Caliban.
But I read somewhere that, every time we see Ariel, Prospero makes it a point to put Miranda to sleep. Ariel is always invisible, said this source I can't remember, and Prospero didn't want Miranda to see him talking to nobody. If that's the case, then Miranda wouldn't even have known that Ariel existed.
Is that right? Takes some of the fun out of the story.