I'm starting to hate the "One Piece seems childish"argument, i would like for some Narutard to tell me why it seems so "Childish"
One Piece.
Features are way too round, bodies are disproportional and the expressions are overly exaggerated, all of those are especially noticeable early in the series. Also early in the series, the drawings have very poor quality. In addition to that, the concept of a crew of "kids" gathering together to chase a dream by becoming pirates is a fairly childish-like concept, much like the fact that, like kids playing pirates, they are not interested in matters of Love and Romance or even ***, even though they are all teenagers when they meet up, with the exception of some later acquisitions. Both Graphic and Concept wise, over the years there has been a very clear evolution, and One Piece began approaching more mature matters, while the general childish-like concept remained very evident, and Oda made sure to keep it that way.
But like many other series/movies/books it is up to the reader the interpretation of the story, and especially good stories allow the reader to scope through various layers of content, and find deeper and deeper meanings. While the childish concept maintains, it is not hard to dig deeper into the matters and find more mature and heart warming topics, which would otherwise seem childish, depending of the maturity of the person reading it. One Piece is a marvelous piece of work, that allows us to jump from dream to dream, boarding matters of great importance and emotional charge, while keeping an active juvenile and free spirit, and that is what makes it so great.
So yeah, I'm using rich words to say that it's not One Piece that is childish, it's you, Narutards.