Check in online before you go.
You can’t get in to your lodge until 3pm, but you can use the facilities on-site from 10am onwards. You could pack all your swimming stuff separately so that you can park up, load up your buggy with all your bits and spend the morning swimming. Then you can send the other half back to the car to drive it onto the village and up to your lodge with all the rest of your gear in, while you saunter over there all casual.
Don’t hurry off to bring your car up to your lodge at 3pm if you don’t have to. Let the rush die down a bit and then go, and you’ll beat the crowds and get a bit more time in the pool.
When you drive your car back to the car park write it down where you left it. That way you won’t have any delays when it’s time to check-out at the end of your holiday! You can leave the site at any time to explore the local area or to do a top up shop. Just let the staff know so you can get a badge for the car to let you back in.
Take a packet of toilet rolls – you’ll only get one roll provided in each of your toilets.
Don’t worry about taking pound coins for the lockers. In most of the villages, everything is done with high-tech wristbands that let you in to your villa as well as your locker. You can’t forget what locker number your stuff is in, either. Just put your wristband up to the little machines in the changing rooms and they’ll tell you. And you can even link it up to your bank card and make cashless payments for food and drink at the pool if you want to.
Take beach towels for the pool. There are plenty of towels at your lodge, but you’re going to want them for baths and showers. And if you forget you can hire one for £2 at the pool desk.
Don’t worry about packing buoyancy aids. There are racks full of buoyancy jackets in two different sizes, and they’re free.
Bring some bubble bath if you’re staying in an executive or exclusive lodge. They come with an amazing bath with bubble jets in.
Take washing up liquid. There’s a little sachet on the sink to get you started, but that’s it. As with most things, you can pick up a bottle in the ParcMarket. But if you’re trying to save money it’ll be cheaper to bring it from home. Likewise, bring some extra dishwasher tablets.There’ll be a handful in the lodge, but they won’t get you through your break.
The rubbish bin is tiny – they’re pretty hot on recycling – so plastic shopping bags are a better size than bin bags. Save them up in the weeks before your break and bring a decent stash.
Take kitchen roll for the inevitable spillages. On that note, take a couple of extra tea towels, too, as there’s only one supplied.
If you want to eat at the pancake house on the last day then get there no later than 11.30. We arrived just before 12 and it was 1hr wait but it was worth it.
Keep an eye out for the baby feeding area in most of the restaurants – there’s a microwave, bottle warmer and baby food pots. It’s free and a really lovely, thoughtful touch.
Cots are good but quite narrow so if your dc moves around a lot in their sleep, use a travel cot if you’ve got one. If you’re going to use the one provided, take small cot sheets. They don’t provide any bedding and in the past the ones that we’ve taken have been too large.
The only thing I would say is that the curtains are very thin, so if your dc needs a dark room to sleep for naps, you may want to take a black out blind and a small night light.

We are going in a few weeks, I'm so glad you asked this as the above comment is ideal!
We will be doing a big food shop and I'll be baking a few bits before we go to make it special.
We play to just enjoy being able to walk at toddler pace without having to rush anywhere (DS is 17months). We have also hired bikes too which we will enjoy.

You asked about spending money and to give you an idea:
A (VERY) small milkshake by the pool costs £2.99
A double G&T at the bar costs £10.00
A hot chocolate on the park is around a fiver
However, if you need something from the onsite shop, go at the end of the day, around 6pm, and you might find some reductions with yellow stickers and THEN you can find some glorious foodie bargains like cakes for desert and sandwiches half off!
You can hire bikes on the park but it’s grossly expensive yet free to take your own. At around £30 for the week to hire one bike it’s probably cheaper to buy and keep a bike rack for your car!
Pack TWO swimming costumes as spinning them dry at the pool costs more money (of course) and instead you can have one on the towel rail in the lodge and one on and keep swapping. Do the same with swim towels!
Bowling worked out to pretty much the same cost as anywhere else which is a turn up for the Center Parcs books. It’s cheaper in the day time (about £25) than the evening (over £30).
The spa is utterly lovely and it IS a treat and not cheap by any stretch of the imagination but it’s a LOT cheaper to go as a twilight customer when staying on the park than just visiting for the day at any other time. For £32 I really enjoyed all the thermal rooms, the pool which is open air and the tranquility of the atmosphere.
Not sure which park you’re going to, but the soft play in the sports cafe is lots of fun but very loud. You don’t have to be a customer to use it which is great but actually I’d recommend buying a coffee and taking the kids to the calmer and way more fun soft play area at Foresters Inn!