That sounds like a nice easy round trip Colin.
Perfect for your first trip to france.
You might find driving a bit more than 2 hours from Ponterson would be good.
Try to get south of Nantes, maybe Saint Gilles croix de Vie. That way you can follow the Vendee coast and avoid all the Autoroutes until you need one.
My parents only live 1 hour north of Oradour and there is a Dutch owned campsite (with a pool) 300 metres from their house. If you are in the area I will give you the address.
If Natasha enjoys theme parks you might want to think about
futuroscope (near Tours)
Also the Aquarium in La Rochelle is very good and well worth a visit. You could overnight right beside it too.