Any chance of adding a couple of days and spending at least two nights in NOrmandy? You can probably find a day trip from Paris but it is a long way and of necessity will give the WWII sites short shrift. If possible train to Bayeux early enough one day to visit the Bayeux Tapestry and then the next day do a day long Overlord tour of the beaches -- they do a great job and you visit Omaha, Iowa, Pointe du Hoc (the most interesting IMHO), Angoleme, the American Cemetery and the Airborne Museum. All very interesting for a history buff.
If you had just one night, you could train up in time to do Bayeux in the afternoon and then do a half day tour the next morning and train back that afternoon/evening.
We like the Churchill Hotel in Bayeux which is near the Overlord pick up spot and the Tapestry and Cathedral. It is full of WWII memorabilia -- pictures etc on the walls and a comfortable friendly place. We enjoyed hanging out in the downstairs parlor where we could get local favorites like Pomeau and cider (they would have soft drinks for the kids).
We spent 5 nights in Normandy a couple of years ago; you can see snapshots of Bayeux here: https://janettravels.wordpress.com/category/normandy/
Unfortunately I haven't put together a post on the beaches yet.