Hi avjerom,
It sounds like you're looking to change the region of a Child Apple ID. If so, first check the information for what needs to be done beforehand below, and found in the article here: Change your Apple ID country or region
What to do before you change your country or region
As mentioned at the end of the article: "If you're a part of a Family Sharing group, you might not be able to change your country or region. Learn how to leave a Family Sharing group."
In this article you'll also see "The family organizer can remove anyone age 13 or older* from the family group. If you need to, you can transfer a child to another family."
If you need further assistance, reach out to Apple Support directly to help. Get Support
Best.