Any suggestions for good places to visit with kids in France?

Just thinking about my summer holiday and we are going to France again. I need to think about day trips and activities otherwise we end up getting bored. Does anyone have any suggestions for cheap, kid friendly day activities? They don’t have to be specific places to go, though those would be nice. I’m also thinking of suggestion for things to do, as well as places to go. For example last year we visited a lighthouse with picnic, a WW2 secret bunker with picnic, a little train ride to a beach with picnic – let’s just say a picnic is a given! We are spending 1 week in Vendee and the rest of the time we are open to suggestions. We will stay in campsites with our caravan and will be able to use our car to get to places.