I've said it before and I'll say it again even more bluntly: if this is to be a whole series of movies based on all seven books (and since Netflix has the rights to all seven, it would seem that's what we can expect), and if they're to bear any real resemblance to what C.S. Lewis wrote at all (looking fairly doubtful with the first one so far, I know), Narnia HAS to be understood as a real place, NOT something imaginary that the children themselves, knowingly or unknowingly, have created.

Apart from the quote from VDT that @col-klink has shared above, there is also the notorious twist in The Last Battle when we find out Susan has rejected Narnia as nothing more than "all those funny games we used to play when we were children". It's a biting commentary on someone trying to be "grown up" in the wrong way and loftily dismissing the things that are truly the most important. And it works precisely because we, as the readers, KNOW that Narnia is real and that Susan is kidding herself. She's basically done to herself, in our world, what the Green Witch tried to do to Jill and Eustace and Rilian and Puddleglum in the Underworld in SC.

Of course it all ultimately ties in with the concept of rejecting God as just a fantasy believed in only by children and weak-minded people — the stance that Lewis himself proudly took as a teenager and young adult, so he does know exactly what he's talking about and why that line of reasoning is so attractive. But this whole essential element of the Chronicles falls apart if we start from the premise that Narnia, nice though it is, is just imaginary, something the children have created themselves, consciously or subconsciously, in order to cope with the "real" world or make it nicer. That's completely contradictory to what the books portray.

I really, seriously, honestly hope the Netflix Narnia film(s) will NOT do that, or even hint at it.