How come in Naruto they call each other by their first names?

So in the Japanese culture they always address people by their last names when their not close. but in Naruto they immediately call them by their first names? at first i thought it was just the dubbed version but when i watch the sub i always hear their first names. Shouldn't Naruto be adressed as Uzumaki-kun or something or Kakashi as Hatake sensei? I don't know this has been bothering me lately.