We’ve done a fair bit of camping with kids.
We use a wind up lamp like a lantern (£10 from Millets) and put it in the top of the tent. Provides a gentle reassuring light for the nipper that seems to last almost all night.
Two and a bit is prob too old for a travel cot. If junior doesn’t normally sleep in your bed, I’d try and get them to sleep in their own bed in their own bit of the tent, otherwise the novelty of it all will keep waking them up. Get a readybed: (http://www.amazon.co.uk/b?ie=UTF8&node=673271011) – they’re also useful when you stay at friends houses.
The nippers are quite sensitive to the cold. Put them in thermal underwear. Then in a big all in one fleecy thing. Then in a snuggle bag. And have a duvet over the top. At least. And, top tip, get a foil survival blanket and put it under the the bottom of whatever bed they are in – only 99p and make a big difference.
Being outside all the time uses up lots of energy. Take LOADS of food (that they like, and will actually eat) with lots of energy in.
Get them a camping chair (only £3 from argos).
Take their wellies. Grass will be wet in the morning even if it doesn’t rain (which it will).
Camping with kids is great. You’ll have a ball.