It's a question everyone is curious to at some point. The answer?
Hell if I know.. The Ramen Guy might have fed him some.. 3rd definitely could have played a role... Iruka? Ehh... Doubt it. But it's possible he did something.
My Question:
If Naruto's mother and Sasuke's mother - at least - were friends and wanted their sons to eventually be friends, why didn't Mikoto or anyone pay Naruto any mind? Sure, there's the fact she never met Naruto. But when he looks so similar to Minato and has the last name Uzumaki? Come on. What - did people just pay that little mind to him? Villagers hated him, though, so you'd think everyone knew who he was.
Just a thought.