Have you read up on the campsite reviews on UKcampsite? They are good for finding out if the toilets never have loo roll or what the shop sells, things you'd wish you'd known. Also look up where there is a nearby camping shop or big Tesco in case you need it.
There's a camping list on this page here
Essentially for our week at half term we'll take
- Big stuff: tent, sleeping things, table and chairs, cooker, cold box
- box of pans and utensils,
- box of food, plus a 5L mineral water
- box of things like torches/wipes/lantern/pegs etc.
Normal outdoor clothes plus wellies, flipflops or crocs and something warm for evenings.
With young children you can't always slope off to the pub of an evening so do pack some wine/beers/chocolate/pringles to while away your evening. The DC will love having treats like cereal boxes or hot chocolate. Ours like camping gadgets like Sporks too. A few glow sticks or night lights in case they don't want to go to sleep in the dark.
Also they will want to let off steam so I try to take a folding frisbee or very lightweight football - basically something they can't destroy other people's tents with. Badminton set can be good, or bikes. They will pal up with other kids on the site most likely.
If your tent doesn't have a porch, lay an old towel in front of the door so that if it rains, there is somewhere for people to come in and take off wellies. It saves you spoiling the holiday by yelling "No boots in the tent!" every 2 minutes. (Who, me?)
We're going for the first time at half term with the dog - that should be entertaining 
