Looking back we seem to have been to quite a few of the places mentioned. We never bother to eat in the restaurants on site:
Lalandia Billund - probably our favourite. The airport is small (so quick to pass through to car rental). Lodges are lovely (once you manage to control the U/F heating), especially if you upgrade. If exploring, make sure you have a parking "clock" for your car. The overnight ferry to Esbjerg is sorely missed. I'm not sure whether you still can, but they used to open up the Legoland Park to anybody for the last hour (so time to fit in a couple of rides and a drink afterwards), which is just across the road. The landscape is less forest than CP and we've not been troubled by midges.
De Efteling (Netherlands) - lovely cottages in the woods next to an excellent theme park - good for all ages. There is a tiny pool.
De Vossemeeren - especially good summer rates if you time it for when the French/Dutch/Belgian children are back at school. Waterpark was a hit. Worth taking/hiring bikes
Duinrell - Great amusement park. Waterpark was really really busy and somewhat lacking in lifeguards. We stayed in some fabulous safari tents. Although we went in summer , the weather was vile.
SunPark De Haan (Belgium). I think it used to be part of Centre Parcs until the group restructured. It is the budget version. A couple of years ago it was looking a bit tired/run down but the location is an easy drive from Dunkirk. Check the location of the lodge carefully, there are dog loo areas alongside a number of lodges (which might not be great in high summer).
We live in the south west so do often get across on the overnight ferry. We usually combine a stay with an Airbnb somewhere quirky (farm/barge/chapel).
We took the Channel Tunnel back last summer and I hadn't appreciated before that we'd be offered an earlier train if we arrived. This was a godsend as it was so wet that day.
For the person whose DH was angling to do AI next year, we did a very cheap package to Tenerife a couple of years ago that included a free pass to Siam waterpark. Thomas Cook aren't around any more but I expect something similar exists.