Joel our 15 year old son rode the practice loop once and then did the 12.5 mile loop. He was toast at the end of it and passed out in the hotel afterward. He only brought one bottle of water with him. I used a camel bak 16 oz up in 2 practice loops of 2.5 miles each. People don't wear armor here on elbows and knees which surprised me.
People do one hill and valley and then stand at the top to consider the next one usually.
Some skilled people ride the whole loop. Bring lots of water and sunscreen. Don't go on the main loop with just one bottle of water- that would be a suicide mission. I would not bring young unexperienced children along here as it takes all your concentration to keep yourself upright. Your brakes and tires will get a significant amount of wear in one day's riding.