Volunteering in Normandy

Are you looking for any kind of volunteer opportunity, or something specifically related to WWII history? Are you also French speakers? While I think it's admirable to want to do good for others, you might find that you create more work for others if you will need a translator to communicate. And similarly to the United States, lots of volunteer organizations in France may require registration and training that would be hard to fit in during a vacation.

Another good option would be to find a French-based organization doing work in the area that interests you, and provide a financial donation. That would allow you to make a real impact in an area that matters to you and would not be time-or language-dependent.

The American Cemeteries in France have an organization you can join and give something back. These are properties that have been gifted to the US by France; you are entering US property when you visit the cemeteries. I don't find any information on line, but I picked up a brochure at one of the cemeteries.

you are entering US property when you visit the cemeteries.

Not strictly true. This from the website of the ABMC (American Battle Monuments Commission). Are the cemetery grounds American territory?
No, the cemetery grounds are not American territory. However, use of the land is granted to the United States in perpetuity, free of any taxes, fees or any other charges. This is done through a treaty between the United States and the relevant host nation. For example, if there is a crime committed within the boundaries of an ABMC site, host nation law applies and the investigation would be conducted by local police.

You could look on the ABMC website linked and see if there's any information about volunteering in Normandy.