Mikoto and Fugaku were the first to find Naruto. They were shocked. Fugaku took it upon himself to protect Konoha and the ninja world by killing the baby in hopes it would kill the juubi for good as it was in a weakened stated having just been sealed. Mikoto jumped in front of the baby and was stabbed by her husband, who was shocked at what he had done as his sharingan should have seen her coming. He asked her "why?" She replied "You or no one is hurting this baby as long as I am alive. This is Naruto! He is one of us. A Konoha villager and soon to be a great ninja just like us. He is the son of our friends!". The wind died down. "You really are gentle" Fugaku replied to his savior wife.
Naruto was taken back to their homes and no one but the few people who were there (Mikoto and Fugaku) knew about their discovery. They raised Naruto as their own. Immediately within two weeks, Hiruzen discovered the Uchihas were holding a baby that might not have been theirs. After a frightening interrogation, Mikoto admitted only to Hiruzen that the child was the jinchuriki. They found him and wanted to protect him from death as he was only a child, an innocent newborn. That was her "alibi". Hiruzen insisted that the Uchiha be put under heightened 24 hour observation at their police headquarters and they were relocated to the outskirts of the village where the River began. Once Naruto reached his 4th birthday, he was considered old enough to live on his own according to the elders and Danzo and Mikoto was forced to sharingan Naruto's memory of growing up with his Uchiha family into nothing. It was a type of amnesia that would sever him from ever knowing them as a family again.
Right before little Naruto is given amnesia genjutsu, Mikoto makes Naruto promise that he will always have happiness in his heart, keep his joyous spirit, and never change.
Naruto grunted and pounded into the legs of Mikoto "I'll never change. I promise. I promise."
Naruto's earliest memory was everyone walking away from him.