How to Book a Flight For a Minor with United Airlines? Under the rules of United Airlines unaccompanied minor policy, which was developed to accommodate the requirements of children, travellers under the age of 18 are permitted to fly without a guardian or parent. You can book travel for the unaccompanied child on United.com or by calling the airline's executive at the United Airlines customer service number. Reservations booked over the phone may additionally be subject to a handling fee of $25 USD in addition to the airfare and the United unaccompanied minor cost.