We're off on Sat (yay) with the dds. I would rather not lug loads of nappies, formula etc with me, so is there a supermarket near the site? (walking distance). Also, can we hire a buggy if dd1 decides she is too tired to walk?
The buggys are wide great for older kids but didn't lie back. Make sure you have credit card with you they take details as a deposit.
A lightweight bike chain can be handy to make sure you get your deposit back. There are loads parked outside each ride and easy for people to walk off with them, or hang nappy with a bit of brown sauce or mustard smeard on it hanging on the handle .
You can buy nappies at cetain shops on site I think and probably in hotels but will be pricey. Tip for cheaper snacks and drinks, there are vending machines at train station which is between park and hotels.
Use the baby swap for biggar rides, you all queue together and say to staff once you get to front. One parent goes on with older child and when they get back they other parent goes, older kid gets 2 shots.