At that age you think you are in love, and probably you really are for all you know; it's just that when you're young feelings come and go more quickly, they're like straw fires, we say in Italy. You often get a crush for someone else on the basis of very superficial elements, like physical beauty, then they open their mouths to speak and you no longer like them. XD

When you mature you start looking for deeper qualities in your partner, more stabile relationships, common values and all that stuff. Despite that, love is a very strange and unpredictable thing, even for adults. Nonetheless, I would consider childish an adult who "falls in love" every two weeks or so.