In reply to sarahjk:
Have you come across futuroscope, in Poitiers? It's about halfway down. Really worth stopping off for - whether you've got kids with you or not.
If it's climbing you're after, perhaps Ceou, although it's well over halfway.
But the blast down is do-able inside a day - this summer we did the Plymouth-Roskoff ferry and drive down in one push.
Martin