According to News Web Easy, a magnet ball is a magnet toy. Its size is around 3 mm to 5 mm. Children are able to play with it making various forms/shapes with a power of magnet.
The accidents of children swallowing this magnet ball by mistake have been continuing. According to the Consumer Affairs Agency , there have been 11 accidents from 2017. There was a case of the magnet ball that children swallowed stuck inside the body and that caused a hole on the internal organs.
As a result of that, the Ministry of Economic, Trade and Industry has decided to change the law and tighten the rule for making and selling of a magnet ball.
The rule to be tighten on those magnet balls which are less than 3cm sized and are dangerous of sticking inside a body because of a strong magnet power.
The Ministry of Economic, Trade and Industry is to tighten the rule from this May.

The image of magnet balls
THE ACTUAL ARTICLE
https://www3.nhk.or.jp/news/easy/k10013965191000/k10013965191000
