This game feels no more childish than most games out there. if you're expecting sophistication out of a videogame story you're looking in the wrong place.
That feels like a cop out for this game's story and writing. It's definitely a lot more childish and simple than most games. Good/Bad writing alone doesn't really apply in this scenario as that's a different topic. This is more of a personal taste thing and I have a hard time getting into more simple stuff, regardless of if it's good or bad at what it's trying to do.