From 0 to 2 years old
On board the aircraft infants generally do not have their own seat but must travel on an adult's lap.

From 2 to 12 years old
They are entitled to a seat of their own at a reduced rate and with the same baggage allowance as an adult.

Unaccompanied minors
Unaccompanied minors (generally between 4 and 14 years old, 12 for some airlines) who are travelling alone must be reported at the time of booking. This automatically activates a special assistance procedure from airport personnel until boarding where they will then be cared for by the airline. The parent/guardian must remain in the airport until takeoff. Similar assistance will be provided on arrival: the minor will be accompanied until they meet with the person named when booking.
It is essential to check the age limits allowed to receive this service as the requirements can vary from one airline to another. It is recommended to contact the airline with which you are travelling for further information.

When pregnant it is always advisable to inform the airline of your condition when booking and request the necessary documentation.