We have just had a week at Ter Spelget and it was marvellous! We chose it a bit at random, as being not too far from Eurosport.
My dc are 11 and 14, so my experience will be different to what yours would be.
It's a massive park, with lots of German, Belgian and Dutch visitors, with a big chunk of Brits. We went the last week of August (cane back 6 days ago) and most dutch/German/Belgian schools had already gone back, so after our first weekend, the park was mostly populated by British families and preschoolers.
My DC loved the independence of being able to walk around pretty safely. They loved the swimming lake (2 slides, but nit really that close), and the indoor pool (one big slide, but also a couple of little preschooler/toddler pools, one with a small flume-slide). Kids under 12 are meant to be supervised by a adult.
They also enjoyed the pump track, bmx track and "midget golf". They were a bit big for the petting zoo, and the organised activities (kiddy disco, kids foam party, some mad thing were they were drumming on exercise balls), craft activities and the gnome walk in the woods over the road.
I loved that there is a really well stocked supermarket on site, albeit a bit pricey, but very convenient. I clocked the 24 hour laundry, but didn't use it. We hired pedaloes and you could also hire kayaks and SUPs. There are sandy beaches around the two recreational lakes.
There a couple of restaurants (one burgers and chips-y, one fancier) and snack bars (pizzas, ice cream) on site too.
We also visited the point where the Netherlands/Belgium and German my meet, which my 11 year old loved!
There's a woodland across the road with lots of (very flat and easy) walks and bike rides. It's a few mins drive from the lovely old town of Ersel (supermarkets) and about 20 mins to the P&R car park to go into Eindhoven.
All the site staff were very friendly and helpful. We had a very chilled time, swimming , cycling and eating a lot of pizza! We were lucky with the weather though. Not sure there be a lot to do in the rain, although on the one rainy day we had, the swimming pool was not packed..
It's a mix of static caravans, cabins, touring caravans and tents, some privately owned, some rented out. We had a 3 berth "cabin" (fancy static!) through Eurocamp. It was an Azure 3. It was nice enough. But the two smaller rooms were very sma indeed! Literally room for 2 small single beds and a locker, plus overhead cupboards. It was a bit like living in an ikea store room set, but it was fine for a week!
I'd definitely recommend it.