Just posting so we know Hercule hasn't killed the thread 
ABF, we love Center Parcs. We're not going to get to go this year I don't think and it'll be the first time in years which will be really upsetting. We always go to Elveden which I think would be your closest too. We've always gone in term time so it's quiet and means that we don't have to book everything in advance and can drop in on various things as and when we like. Alex loves the crafty sessions and Catherine really liked the soft play last time we were there. We do lots of swimming which Alex really likes and the pool there is great with lots of areas to keep you busy. The main pool has a wave machine, there's a lazy river, lots of flumes and slides and even a toddler area with mini slides and shallow pools which they keep extra warm to stop the little ones getting cold - although we do still take neoprene suits as my skinny children get cold easily! We take Alex's bike and it's great to let him tear around without the constant panic about roads (although there are still CP vehicles so watch out) and then we pay for a few eaxtras like bowling and crazy golf. Alex tried short tennis for the first time last November and really liked it. There's loads of nice places to eat including Hucks which do a buffet type hot meal for children (chips, burgers, fishfingers, beans etc) so they can eat immediately and then run off to play in the play area while you take your time :) All the resaurants have play areas which is great, I don't know why normal restaurants don't have them, we'd go out a lot more often if they did! Get one of the newer style lodges as they're much nicer and make sure you pick up some of the crackling logs packs so you can cuddle up with a movie in front of the fire in the evening. I always make food cheaper by taking loads too. I like making a big lasagne or something before we go - I freeze it then it defrosts on the way there and we get an easy meal on our first night.
I'd definitely recommend it 
Catherine is trying loads of words at the moment. She says 'Shoes', and 'hello' and 'tree'. She does a good monster growl too. She's so much fun at the moment.