In reply to TobyA:
Honfleur is worth a visit, nice old port, Normandy beaches in a fairly particular sense as most of the visible history is WW2, pleasant but not particularly dramatic coast. Falaise, of William the Conqueror fame is pleasant in a bucolic sense but what they call the "Suisse Normande" is to be taken in a very relative way.
If you can go a bit further the Cotentin is already a bit wilder, with more spectacular views and then Mont St Michel is very special but crowded in Summer, and St Malo with it's granite wall well worth a visit. Further West gets you into a different country, Bretagne, with it's own Cornwall and the most spectacular coastal scenery I know the Pointe du Raz... the force of the tide flowing past and the granite cliffs and islands is exceptional, quite frightening even at a distance. Inland their are many ancient forests with all sorts of Arthurian places which should please the children.
All in all a week is about right for a good visit, the green Michelin guide is as good as any for both Normandy and Bretagne.