We stayed in a Centre Parcs in the Netherlands last year. De Eemhof. It's quite close to Amsterdam itself, and also Utrecht (lovely Uni city) and the Zyder Zee inner causeway (we drove over that to get there from Medemblik where we had been for an event). (DH also wanted to explore Almere, as a city that was designed from bare fields in the 1970s' - the excitement
- but it was also a big sporting city so DD had a great time buying lots of sports gear there). We rented a car in AMS on arrival, spent a day in Utrecht, a day in AMS city itself (and could have easily done at least 1 more day) and also relaxed in CP itself. There were boats to rent there, and bicycles (DH enjoyed both walking and cycling from De Eemhof along the dyke beside the sea that is now a lake). Netherlands was a very relaxed country too.
DD was 13 while we were there, so younger than yours, but we felt we could give her great freedom there. CP itself is a little tired and dated compared to Sherwood or Longleat (the ones we've been to in the UK) but accommodation was fine and we had a nice cabin right over a lake with lots of interesting wildlife to watch from the deck.
But it was also the first time we'd left the CP site when we stayed there - there are the usual activities (some paid, swimming is free) but as we had done a lot of those before, we got out and explored the country instead. But there were still activities to do on site and that we could let DD head off to herself too.
We had liked the look of some of the other CP sites, but picked DE because of its proximity to other cities. And we had been up north for our 1st week.
Driving in Neth was really easy - I normally leave the continental driving to DH and just do one journey to be able to if there's an emergency but I did loads on this trip. We flew in and rented a car because it worked well for us, but there is also a ferry if you wanted to bring your own car and lots from the UK had done that for the event.
Food was good, both eating out and supermarkets. Beer was good. Lots of low and no alcohol beers available in pubs. We ate in a Michelin Bib restaurant 1 night in Medemblik, which was divine, and cost us the same as a very ordinary meal back home (€50 for a 6 course tasting menu including the wines!!). We BBQed in CP a lot as that suits us but there was plenty of places to eat that looked fine there, and we had also eaten out when on our city visits.
Amsterdam is lovely - there is so much history. The canal boat trips are great to do for 90 minutes or so to get your bearings but not so long that teens should be completely bored. Book the Anne Frank house in advance - we didn't get there this time (we'd been before but had hoped to bring DD this trip as she hadn't been). There are art galleries, sports grounds, Heinekin factory tour....all sorts. And some interesting shopping too, which might keep teens interested.