Kinsley goes there:

[E]xtend the franchise to children, but let parents vote on their underage children's behalf. In effect, parents would get an extra vote for every child. How would this solve the entitlement problem? It wouldn’t, directly. But it would revise the allocation of political power to more closely reflect who has the most at stake. It would reward long-term thinking rather than short-term thinking. Right now seniors are all-powerful because they vote in such large numbers, while young people must rely on the good will of their parents and grandparents to protect their interests. Every politician invokes "our children" as the most important consideration on every issue, and then, having done so, is free to ignore them.