Child Voting

I don't think the issue is as clear-cut as djw and Matt make it seem. To be sure, djw summarizes a persuasive article in favor of it - a very persuasive article in favor of it - but I'm still skeptical. For one thing, I think that it's important to make it clear that universal suffrage for under-18-year-olds is just plain silly. For one thing, there's the logistical matter - infants aren't very good at using Play Doh, let alone using a Diebold machine. Moreover, even if they are able to work the machines, their votes would be pretty much random, unless they're directed by their parents - voter fraud! And though random voting is a cool way to screw over classmates in a student body president election, presidential elections are too important for that.
So, if we've established that there should be some age restrictions for voting, it becomes clear that the distinction between 17 and 18, or 16 and 18, etc. is pretty arbitrary. There's no significant reason to choose one over the other; there was a compelling reason to choose 18 over 21 during the Vietnam years, when people who couldn't vote were being killed for no reason, but even then it would have been easier, and just as sensical, to raise the military entry age to 21. Matt's argument that allowing 16-year-olds to vote would create a more civically aware populace aside (though I do think it's reasonable and probably correct), it's simply too difficult and not worthwhile to amend the Constitution to change the voting age by a few years.
For an interesting, more emotional argument in favor of children's voting, see François Truffaut's excellent L'Argent de Poche. The circumstances around the argument are central to the plot, so I won't reveal them, but it's really a quite extraordinary piece of rhetoric from an extraordinary director. In fact, I'm surprised that neither djw, Scott, nor Bob from LG&M mentioned L'Argent; they're quite the film buffs.