His childhood name, the Prince Oama (Ohoshiama, Osama), which he used until he ascended the throne, was related to the Oshiama clan (they worked as the chiefs of various departments at the Imperial Court for the Amabe clan) that took care of him when he was a child, and it was the custom of that time to take one's childhood name from someone who brought one up.
即位前の名は大海人皇子（おおあまのみこ、おほしあまのみこ、おおさまのみこ）といい、幼少期に養育を受けた凡海氏（海部一族の伴造）にちなむもので当時では養育者より幼名をとるのは慣例だった。