We call these tiny ball of rice cake "Gyungdan", traditional Korean dessert.
They are made with rice and rolled into a various powders.
How to make them?
Have some sweet rice four, mix with boiling water.
Yes~! boiling hot water for sweet rice four.
Make a small ball and boil until they float.
Drain and roll into the powder of you choice~
I love ones covered with powdered pound cake.
Traditional powder is (baked) soybean flour, sesame powder, black sesame powder, red bean paste, chestnut paste etc...