Children under 6 years of age travel for free. If the child does not yet attend school, he or she must be accompanied by a person over the age of 6.
Children from 6 to 14 years of age have their own single tickets, a special stripe ticket rule and a children’s day ticket.
For young people aged between 15 and 20, there is the U21 offer: you use a Stripe Ticket but only have to validate one stripe per zone. So you only pay half an adult fare.