Went twice, first time fly-drive, into Carcasonne and a capsite near Valras Plage (forget the exact name), just below Beziers. Lovely site, went Keycamp so a bit dearer. Best to book direct. Found the Ryanair luggage weight thing a pain.
With kids I definitely think you need a car (muesli & sandals in the bin
).
2nd time went with caravan via UK to St. Jean de Monts. went in June so was a bit quiet (smallies not in school), would go July or later anymore (especially if bringing own accomodation the rate increase is nothing much). Great holiday, but a long haul driving. This year Cornwall !
Have gone off the idea of flying as now 2 small kids, so much hassle & when you add in car hire & accomodation the road option starts to get competitive.
Would love to get a reasoable ferry with caravan from Cork or Rosslare to France but consistently get quotes of about €1,800 which I think is OTT.
If I was you I'd bring your car on the ferry, book your own campsite, do 1 hard day's driving and get down a bit south for the sun. & last tip, stock up on food before you get on the motorway, selection is apalling in the motorway shops.