You could tour the Netherlands. It is compact, so you can see a lot in just a few weeks.
I like camping Witterzomer in Drenthe. Website is only in Dutch I am afraid. Lots of things to do for kids, such as small lake with beach with play equipment, swimming pools, mini golf, pony riding, several playgrounds, kids clubs, bicycle and tricycle rental. There are various other things to do in the area, such as Verkeerspark Assen, Observatory, etc.
I also like camping de Noordduinen, if the weather is nice you spend the whole day on the beach, if not so nice you can still go and look for shells and drift wood and walk to Noordwijk (nice restaurants, shopping etc). Also close to Leiden (very pretty and lots of musea), Delft (beautiful old city and lots of things to see), The Hague, Scheveningen. Amusement park Duinrell is not too far either. You can rent bikes on the camping and by bike you can go to many places, cycle paths are excellent, you can also cycle along the coast through the dunes to other coastal towns.
Best amusement park for kids in the Netherlands, possibly Europe, is the Efteling though. It is huge, truly huge, way bigger than Disneyland Paris. This mini camping is a very very short walk from the Efteling. Camping is basic but adequate and cheap, also short walk to Kaatsheuvel to do shopping.