Yes. You may use the app on all devices associated with the app store account that purchased the app, of course. But your children may have their own app store accounts, or you may want to share the app with other close family members. Fortunately, all of the app stores that sell the XtraMath app have programs that allow you to share apps with family, and we participate in all of them.
Learn more about Apple’s Family Sharing program.
Learn more about Google Play Family Library.
Learn more about Amazon’s Family Library program.