It depends like if it's a big group then it could last for about one hour to three at the highest , but remember that your child has to be in a high level like level 3 you could try your most of...
I assume you mean The Ironman Triathlon. It consists of a 2.4 mile swim, 112 mile bike segment and a full marathon of 26.2 miles for a total of 140.6 miles