Child fare applies from 4 up to and including 15 years. Children under the age of 4 travel for free.
At 16 you are no longer entiteled to child fare, and it is your responsibility to change your ticket.
Remember that you must be able to show that you are entitled to a discount upon request. Passengers who fail to produce a valid ticket during an inspection will receive a fine.
Saturdays, Sundays and Norwegian Bank Holidays (except May 17th), you can bring 4 children for free on travels in one zone with any adult ticket.