These items are purportedly toys that belonged to Prince Shōtoku when he was around five or six years old. There are sixteen of these cubic crystals, which are stored in a case made during the Edo period. They appear in a Heian-period work of historical literature called the Eiga monogatari and may have been used in a board game. It is also possible that they are the precursor to a game known as otedama. According to the latter theory, the name can also be read as ishinago. In that game, stones would be placed on the floor, and then one thrown into the air. The player would then attempt to grab a stone on the floor before the airborne stone fell, and then they would catch that stone before it hit the ground. The number of stones would be increased by ones and twos, and the person who could pick up the most stones would win.
That being said, it is unclear whether these objects were actually used as toys.