about Underage purchase of gaming equipment on the App

Hi，From September 13 to September 29, my son （10-year-old ）bought a lot of equipment on the APP and spent ¥162,000JP. I did not know about it，so I wanted to apply for a refund ，How should I deal with the refund? how can i connect you？ My family is not rich, I hope your support，thanks very much.