You can request a legal change of ownership, whereby your children are credit-checked and the phones are transferred into their names. The process is explained under "transfer to a friend, colleague or family member" on https://ee.co.uk/help/profile/manage/change-my-account-in-the-case-of-a-life-event
You'll lose the ability to share data between phones that are currently on the same pay-monthly billing account.
