Advice:
Make certain they drive through Chartres. The Cathedral has been cleaned up and is very nice.
While in Brittany stop and taste the ciders. There are many places to stay near Mont St. Michel.
Last summer while driving from Mont St. Michel to Normandy we avoided the autoroute and took the state roads that parralled it. We have a great time seeing the smaller towns, stopping in Lisieux, had a great lunch in a tiny village and my sons played fussball with the local mechanics.