When they approach YOU and want to be a part of the finish because they think it would be cool and they see other kids doing it AND you can do it in such a way as to not impact others enjoyment of the event, it gives you the opportunity to give them a little bit of fun in what is otherwise a very boring 5 days ... and if it is sanctioned by the event and you're doing it with consideration for others where is the harm?
Again I fully support regulating it, including numbers, ages, separate finish lines, etc., but just a big blanket "throw them all off the pier" is plain silly. Like it or not, it has become an integral part of the event. If you think there is demand, go ahead and start a new iron-distance race "The No Family in the Finish Chute 140.6-Man". I'm sure people will come from all over for that one.
"Knowledge is good" - Emil Faber