The local town is nice and has a good market - we take our bikes so I rode up there with DD and we had a mooch around. We did a few other rides too, the Loire is great for cycling as it is flat (!) and has lots of signposted routes.
We also went off somewhere (not very far, can't remember the name of the place, but reception gave us the details!) to do kayaking which was fab. You would be able to go in one as a family and it was very safe.
We had a day in Tours, which is quite a nice city.
In previous years we have stayed on other sites in different parts of the Loire and there are lots of good chateaux to visit. Cheverny had a TinTin exhibition when we went (both DC are fans!), another had a huge leaning!) pagoda in the garden that you can go up, another hosts a big gardens exhibition with loads of interactive stuff for children.... I will see if I can find the names of them!
We also have done quite a bit of wine tasting in the region - there are lots of "caves" and vineyards you can visit
We are going in earlyish August (after 10 days in Brittany). It was very hot last year, hope it's just as nice this summer! Where are you going in the Vendee? We have been there too!
Also have you heard of Puy du Fou - it is sort of between Vendee and Loire and is absolutely fantastic - a re-enactment theme park.
We went to Futuroscope last year - a sort of collection of 3D and 360degree cinemas and some rides. DH and the DC enjoyed it more than me!