Depends whereabouts in France of course, but we have had lovely holidays in Brittany here www.camping-bretagne-atlantique.com/piscine.htm. The campsite has swimming/paddling pools, a mini farm, campsite based in an old orchard, with hedges between the emplacements and best of all, IMVHO, a 5 min walk through a lovely wood to get to a stunning, shallow sandy beach. You can hire bikes and cycle round the local lanes and there is a Breton festival just at the end of the road in August. lots of activities, probably more for older ones.
The pizza takeaway in Fouesnant is fab (opposite the tourist office) and there are lovely sheltered beaches at Cap Coz and night markets etc locally. We like to head round to Concarneau, which has a port with clippers and fishing boats as well as an impressive city-fort in the harbour to wander round. There's a lovely creperie in the Ville-close, one of the best we've found in Brittany. www.creperie-lepennti.com/
There are artist villages close by to wander round, fishing at the Point Mousterlin, we've done daytrips to Brest Aquarium Oceanopolis (well worth it) and the Breton village museum Poul-Fetan sagemor.com/visites-animations1.html and Carnac standing stones.
Alternatively, we had a super short break here the year before last www.campinglavallee.co.uk/, 1 km away from the beach in Normandy. We took the children to the races at Dieuville, pottered on beaches, visited Pegasus bridge and went on the little tourist trains in the Edwardian style resorts. very relaxed atmosphere.
Or for a very different place www.camping-le-ruisseau.fr/ this is in Biarritz and you can travel into Spain to Bilbao or take the children to the many large caves with evidence of neolithic dwelling. Campsite is lovely, has animals to visit (poneys to feed etc) and a super paddling pool complex. Very different feel to the Med, fab food.
We tend to take the Portsmouth - St Malo ferry as it means it's only about 6 hours drive to Biarritz from there.
The Castels and Camping website gives some family-based campsites which are quite luxurious/'safe'. Can be pricey.
Hope this gives you some ideas.