We take our 3, the youngest was 2 when she first went. Shes now 7. We take them to the SE corner but late afternoon, early evening when it's a bit quieter.
Also, cook breakfast as others have said and as there is so much good food, share main meals so they get to try lots of different things. Carry the stainless steel water bottles round to refill for free at the taps/water aid points.
Have a nap in the afternoon means they can stay up later.
Don't over pack as ours tend to wear the same things unless it's a really wet one (which it won't be)