My son can log in to the iCloud but not the App Store.z

when trying to download an app or sign in to the App Store/iTunes through the settings area I am asked for my id and password. After entering it and clicking sign in it immediately goes back to either "get" (in App Store) or "sign in" in settings. Everything was working fine until this evening. I've tried closing and reopening the app, shutting down the iPad and signing in and out of the iCloud to make sure the id and password are correct. Is this an Apple issue?