When booking the flight ticket, it is important for you to mention that your child is travelling alone. The airline will then give you instructions and advice specifically on your child's trip. The policies, such as age limits and prices, vary by airline
Accompanying the child to the plane
A child travelling alone may be accompanied through the security check and to the departure gate, when the boarding pass is marked with the status "unaccompanied minor". Sometimes this is marked with the abbreviation UMNR, UM or UMI.
You will get more information when you arrive at the airport's check-in with your child.
If the destination of the flight is outside the Schengen area, the person accompanying the child must also have a passport with them.