On Ryanair, the seating of children is governed by a strict Family Seat Policy designed to ensure safety and group cohesion. Children under the age of 12 must sit beside an accompanying adult who is on the same booking. To facilitate this, it is mandatory for at least one adult in a family booking to purchase a reserved seat (typically starting at a few euros). Once the adult selects their seat, Ryanair allows up to four children (aged 2 to 11) to receive a reserved seat next to that adult for free. If you do not follow this process during booking, the system may separate your party, and you might be required to pay for seat changes at the airport. For teenagers aged 12 to 15, sitting alone is technically permitted as they are not subject to the mandatory "beside-an-adult" rule, but they still cannot travel as "unaccompanied minors"; they must be on a booking with an adult aged 18 or older.