We first did it at 15 months. Rose was fine with it. Lots of friends have done it much earlier, we didn’t for various reasons partly just cos of the time of year she was born making it less attractive.
We took the travel cot (Phil and Teds one), that was handy, to stop her roaming in the night. I know of people who sleep their babies just in the main tent with them, depends on how much of a wriggler / escaper yours is, and how much you enjoy having a small over-excited gigantic slug-like sleeping bag creature crawling over your face in the middle of the night.
Done it twice, once with tons of gear, car camping, which was nice, nice to have nice meals, a table to eat off, double ring cooker etc. Second time I did it lightweight with her in the bike trailer, and my 2 man ultralight hiking tent. That was brilliant too, slightly different (we went for cold food / pub meals), but easy enough to do.
Pictures of the bike trailer trip here (you shouldn’t need a facebook account to seem them)
http://www.facebook.com/media/set/?set=a.10150381323769388.408411.635999387&type=3&l=07049df796
Rose loved it both times.
It makes a big difference if you have a good sleeper – Rose is very energetic, which means she goes out like a light at the end of the day. Not the easiest to get to sleep, but once she was gone, she was down until 6.30 or so. If you don’t, you might have a real nightmare, particularly if there are any other kids around who can get woken up by them / vice versa.
Also, if it’s the middle of summer, expect them to wake nearish to dawn and plan accordingly (ie. work out who is going to take them for an early morning walk so everyone else can sleep!).
Oh, the only super vital thing (other than obvious things like nappies etc.) is a rain suit or rain trousers/salopettes. Even if it doesn’t rain, there’s usually a lot of dew around to fall over in, and if it does rain, kids don’t understand about sitting in the tent reading a book. Wellies if they walk too obviously.
If there’s only one of you taking them, don’t forget that this basically means early nights, or at least back to the tent early. I don’t find this a problem personally, especially if I know I’ll be up at 6 the next day anyway!
Joe