well there are seven books in the series, and i think only books two through five have been made into films? anyway, in The Voyage of the Dawn Treader only the two younger children return. in The Last Battle however, the eldest son is back but the eldest daughter is not.
The Magician's Nephew is counted as book one these days, but that was not the order in which it was written and a few things won't make as much sense if you read it first, so I'm not sure why they re-ordered it other than they think that chronological order makes more sense overall, something I disagree with. It was originally the penultimate book, before The Last Battle.
So really, one through four were made into films, but BBC TV and Radio both did the whole thing.