Rita, not only do most kids not do the training to handle a marathon. Those who do would still be better served running shorter distances. As for the “until they are out of college” thing, that's absolutely the right choice if they are going to be competing for their schools. The collegiate racing season already drags on through most of the school year. The last thing they need is to extend that by fitting a marathon into the year somewhere.
Andrew, great point. If there were any relationship between marathon participation and obesity, it doesn't seem to be the one that these people are suggesting (in my opinion, great evidence that there is no relationship). It doesn't have to be all or nothing. In this case, the most ideal place is the middle ground.