We were originally going to go to La Yole in St Jean des Monts, but found we could stay in Sol des Gogo, to be on same site with family, but it wasn’t an ACSI Camping Card site. Consider joining ACSI.eu ..Camping Card as it pays for itself in reductions in a few nights. They quote 2adults, Electricity and showers generally less than €19, don’t know how much when there are children...some sites include children free. This year Ireland had 12 sites, it was 16 in 2017, all sites are €19 (except Apple Farm €15) (don’t take dogs)
ACSI Reduction only applies before first week in July after late August.
As mentioned above Aires are good too.
It is pity you can’t stay longer than 8 days as it takes a day beginning and end on ferry....and as mark&Wendy said costs the same...price goes up in higher season.
We did our first holidays of many holidays in France (car/Eurocamp tent) was when oldest was 6 (now 38), he was a Eurocamp courier when he was 20.
If going to and from France between June to Aug, on Irish Ferries or Stena you get a free trip to UK....after Aug. when you compare French crossing 17 hrs and cabin, it nearly costs that on 3.5 hr sailing, no cabin to UK.