Onigiri (toy) - Onigiri

Japanese: おにぎり（玩具） - おにぎり

…At this age, children have the habit of putting things in their mouths and sucking them, and in order to develop their sensory organs, they are designed to be played with by sucking, hence the name. Many of them also serve as rattles, and those that can be held in the hand and shaken are called "onigiri." Since the Edo period, there have been wooden turned products. …

From [Rattle]

…It is called onigiri because it has a round handle and a ball inside, which makes a rattle sound when shaken. Some also serve as pacifiers, and those that can be held in the hand and shaken to play with are called onigiri. It is said that in Japan, it began during the Muromachi period when court ladies at the Kyoto Imperial Palace made paper onigiri. …

*Some of the terminology that mentions "onigiri (toy)" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…この年ごろには，口に入れてしゃぶるくせがあり，感覚器官を育てるため，しゃぶって遊ぶように作られているのでこの名がある。がらがらを兼ねているものが多く，手で握って振れるように作ってあるのは〈おにぎり〉という。江戸時代から木製挽物（ひきもの）細工のものがあった。…