I strongly recommend Camping Du Letty in Benodet. We discovered this site on our first trip to France 10 years ago. We have returned, latterly as caravanners, on 5 of the subsequent years - our 5 kids always protested if we went anywhere else!
The beautifully maintained site is large but divided up by hedges into shady bays of c.8 pitches. Some pitches overlook the beach. The site is adjacent to a small, tidal river estuary which provides a large, clean & safe beach and swimming spot at all but high tide. Many campers take boats, all sizes, which can be launched/moored free in the river.
The site is quiet and peaceful with excellent facilities away from the pitches. Including small supermarket, 2 bars, a gym, library, tennis courts and playground. There are a few arranged activities. Our kids always entertained themselves - mainly on on beach and sea/river. The site is featured in the Alan Rogers guide and it has its own illustrated web site (search for du letty)
Benodet is a pleasant, picturesque seaside resort at the mouth of the river Odet. It has supermarket, shops, cinema, restaurants,marina & even Church services in English!
Roscoff, nearest, is less than 2 hours pleasant drive away but it gets booked-up quite early. We have, also, travelled via St Malo, Cherbourg and Caen. The AA website free provides route plans to Du Letty from all 4 French ports
We booked our ferry through the Camping & Caravan Club (reduced) price.
Site booking is not necessary as they always have room, even in high summer. We didn't book on first & several other occasions. Direct booking is cheaper than holiday companies.
Give me a ring on 01744 27962 if you'd like to ask anything more.