Absolutely not. Children (and even teens) are not nearly mature enough to vote. Even a lot of 18-year-olds are not mature enough!
Example: I remember the school election we had my junior year of high school. A bunch of seniors ran for president, which led to a "primary", elimination of all but the two highest amount of votes, "speeches" (if you can call them that -_-), and the election between two candidates running for each position. The race for president was especially interesting. It was between this one kid who was a bit of a jerk, but was normal for the most part, and a kid who was clearly in his own world 100% of the time and almost definitely crazy to one degree or another. We'll call them Jay and Bob, respectively. Jay went to classes and campaigned like any other normal human being would. Bob stood at the front of the school in the morning and shook the underclassmen's hands when they walked in from the bus, but didn't even mention the campaign.
A few days before the election, we were discussing it obviously. This is where I learned that basically every single freshman was going to vote for Bob based on "He shook my hand! He's funny!" Much of the sophomore vote was similar, I'm sure. And even some juniors thought "We should vote for him. What a joke! It'd make the position very interesting for the next year."
Then we voted, and I know for a fact that Bob won. But when announced, Jay was declared the winner. And later on in the year, a story went around that Bob crashed his car into a tree and went to the hospital (unrelated to election result). Apparently he really was crazy and I don't remember seeing him in school after that.
And that's what children and teens think of when voting. Therefore, bad idea. The second a celebrity endorses a candidate, the children will agree with their favorite celebs, or their friends, or (God forbid) their teachers, who shouldn't even be discussing politics in school. Nevertheless, 18+ for voting.