DS LOVES to ride his bike. He's on two wheels without training wheels, and is almost ready for some easy trails. We regularly do 5-6 mile bike rides with him and he's usually raring for more when we cut him off. He's awesome with that thing. He turned 4 at the end of April.
I found this Duathlon (http://www.triitnow.com/KCD/kidscandu.htm) happening on August 4th for 5-10 year olds. It's extremely short. A 200 yard run, a 400 yard bike, and a 200 yard run. He can run a mile, so none of this will be difficult for him. His biggest problem would probably be the crowds of bigger kids on bigger bikes (he's on a 16") and remembering all of the rules of transition. The website says to call to ask about special arrangements for 4 year olds. I'm going to call tomorrow, but do you think it means just getting permission to race, or would we be able to give him extra support through transition? Not touching him or anything, but giving reminders of what to do.
I think he would have a TON of fun doing it. He can put on his helmet and take it off all on his own, but I'd hate for him to get disqualified or something because he, say, forgets to get of of his bike at the dismount line. He's 4, so it's not like he'd be actually racing for anything other than doing it.