We went to a place called Domaine Des Ormes, Dol de Bretagne, Brittany a couple of times when the kids were younger. There were 2 fishing lakes with loads of daft french carp to catch. There was plenty to do on site and also a golf course.

Try a post on pechemaniac.com, a very nice French forum. Google translate will help. I can also recommend Carnac although it may be a bit of a drive for you. The river blavet has some good fishing and there is also the Nantes breast canal.

Hi, I used to holiday for years in Brittany and when I got there I would purchase a 2 week permit which I got from a local shop at a place called Jugon les Lacs.It was a holiday permit called permit de vacances I think, can’t remember the correct name.
Although I used to fish the lake a lot the permit had a map with loads of lakes,canals and rivers to fish.
Usually the lakes you could drive upto and there was usually a playground or a restaurant close by for the missus and kids.
Great fishing to be had as good as Ireland in its heyday IMO.
If you can find a tackle shop local to where you are staying they’ll give you plenty of info.