Earlier in the year when we visited Normandy we stopped at a beach before boarding the ferry at Cherbourg. You may have experience of arriving early for a ferry, in which case you know that after an hour 'i spy' starts to wear a little thin.
We headed just a few miles from the Cherbourg ferry terminal and found a lovely sandy beach with plenty of small rocks to clamber on. There were some huge shells to be found too - we've not seen shells so big before or since!
Head west from the Cherbourg Ferry Terminal roundabout on the N13 and take the first exit on the second roundabout to Boulevard de Collignon. Along this stretch of road there are a couple of car parks you can use on the beach front. It's a perfect spot to kill some time and expel some energy before catching the ferry. Perfect for those travelling with kids / dogs / annoyingly friends.