Q: Cancel my payment method cause my kids are using it without my permission

See here: Change or remove your Apple ID payment information - Apple Support

Family Sharing and Ask to Buy may also be worth looking into. -AJ

This below article might help you in preventing kids purchasing with out your consent

Use Restrictions on your iPhone, iPad, and iPod touch - Apple Support

If family sharing is present this below article is also an one of the helpful article.

Request and make purchases with Ask to Buy - Apple Support