Kids can't vote for the same reason they can't do lots of things: because millions of years of human history informs us that children aren't capable of looking out for themselves. They need adult supervision. We make the same judgment toward others who are deemed unable to look after themselves — the mentally ill, elderly people suffering from dementia, etc. — so this is hardly something unique to children.Karl Smith also got in on the Kids Vote fun.
But we don't treat these the same as the voting case. We do let children have bank accounts and invest money and have all sorts of other adult activities; we just require that a parent or other responsible person act for them as their agent. Voting is different; we just don't give them the vote at all.
As I said last time this came up, to the extent that we think of politics and democracy in liberal, Lockean terms -- democracy is justified because it allows everyone's interests to be represented -- then I really can't see the case against vote-from-birth, with parents administering the vote up through some at least teenage years. My view is that we think it's weird because we don't have it, but if for whatever reason vote-from-birth had been instituted centuries ago we would all find it perfectly logical and regard any attempt to take it away as outrageous and anti-democratic. The only question would be at what age it's appropriate for kids to begin voting for themselves...there are a lot of reasonable ways you could handle that: a fixed age rule, a fixed age rule plus some sort of test-in for those below that age who want to exercise their own choice, or just leave it informally to each family to deal with it on their own. Longer liberal argument for vote-from-birth here.
On the other hand, I do think there's a reasonable argument against vote-from-birth grounded in more republican views of politics. If justifications for democracy are based on the inherent value of political participation, then it makes some sense to exclude those who cannot "really" participate because they're not yet able to appreciate the experience. However, voting itself is relatively less important in that version of politics, and in my view is best seen as sort of a training wheels introduction to real political action -- and therefore, I think, quite appropriate for high school kids and perhaps middle school kids.
The only version of democracy that clearly doesn't support an expansion of the franchise from where it is now would be a good government version that justifies democracy on the basis of informed individuals, thinking for themselves, being the best way to make good decisions about public policy. Allowing 14 year olds to vote makes no sense in that version of democracy -- but then again, I think it's an entirely mistaken version, so it doesn't carry any weight with me at all.
On the practical question, if you can call speculation on the effects of a reform that's not going to happen a practical question...
Kids Vote supporter Matt Yglesias said over the weekend that he would expect turnout for children to be low, the way that the youngest voters now have the lowest turnout. I'm not sure that's true, even given the rule of allowing kids to vote only for themselves but as soon as they choose to do so. In practice, what you would get is turnout up through at least high school that's driven almost entirely by parents' decisions. Now, it would be capped at parent turnout levels (except in the extremely unlikely case that schools organized it as an in-school activity), since not too many 7 year olds or even 14 year olds are going to go off to vote by themselves. But I'd guess that quite a few parents would make it a family activity, and virtually all politically active parents who vote by mail or absentee would also have their kids vote (that is, vote for them). My guess is that turnout for 6-12 year olds would be quite a bit higher than current turnout for 18 year olds. On the really speculative side, one might think about two things: whether voting early would make party even more inherited than it already is, and one also might think about how acquiring the voting habit early in life might affect turnout for adults years later.
The other question here, one that is obviously relevant to the (non-existent at present) hopes Kids Vote has of actually getting mainstream political support and being enacted, is partisan or political effects. Jonathan Bradley tweets: "Isn't the political system biased enough in favor of families?" It's true that anything that makes people more settled tends to increase voting turnout and participation, so it may in fact be true that the political system produces a bias in favor of those married with children over young singles -- but I'd say the more important bias in the system is in favor of older people. Of course, any kind of successful franchise expansion depends on a sort of oddball circumstance, in which the people currently in office believe that they will be helped, or at least not harmed, by enlarging the electorate beyond the people who voted for them in the first place.
Just to be clear: I'm at this point in favor of a lower voting age, and haven't heard a winning argument against going down somewhere around 14 give or take a couple of years; I'm intrigued, but not entirely sold, on vote-from-birth. And I'd either abolish completely the minimum age for holding office or set it at the voting age.