On the night of the kyuubi attack two children were born a boy and a girl. Naruto and Mito Uzumaki-Namikaze .
Minato sealed the power of kyuubi into Mito and the souls into Naruto. Would they have neglect Naruto to train his sister to control kyūbi's chakra.
I don't own Naruto. All rights go to Kishimoto Masashi