We went to Camping De Paal, just over the border with Belgian (it's in Holland). The website is in Dutch but don't let that put you off - it's fab. They speak faultless english if you email or call. Great pool with water play area (never seen anything like it); big playground plus play areas on each field (individual plots are generous - most people have campers or caravans but we were camping and there were lots of tents too). Bike hire, children's farm where you can get the rabbits out ... etc etc. Really good facilities for washing etc - cleanest I've ever seen on a campsite. Properly hot water and baths!
The restaurant was a bit rubbish but I couldn't fault it otherwise.
We drove from Calais but broke the journey near Bruges - but you could easily do it under 5 hrs from the ports. Probably about 3 hours.
We've done Durinell with eurocamp (in the tents). I thought the tents were great. In hindsight the site wasn't really appropriate for the age of our dds when we took them (1 and 2) it would be great to go with 11+ year olds, you would basically never see them there is so much stuff to do in the theme park.
It is basically like camping in Thorpe Park.
The loos were AMAZING. They were so clean and sparkly. I swear there was one lady who was just permanently cleaning them, like the 4th bridge.
You could try Camping Konigshof near Leiden in Holland. Has an indoor pool as well as an outdoor one, clean loos, showers etc. Easy to get to from Hook of Holland via Harwich & good access to Den Haag & Amsterdam.
koningshof is very small though. I wasn't impressed. The shop is ok, but the only restaurant on site is quite pricey too.
I went to a lovely one in Germany with eurocapms, where we had a fantastic time. sudsee camp The lake is beautiful, it has great facilities, reasonable food. Its a bit further from calais, but the german road system is great.
Great to hear duinrell is good, we're booked there for easter.