Infants up to the age of 3 can travel on an accompanying adult's lap for free, however If you have a child over the age of 3, or have an infant occupying a separate seat an additional seat must be purchased.
Children under the age of twelve (12) and a height less than one hundred and fifty (150) cm should have children safety seats suitable for the size and height of children. Children under the age of three (3) years cannot travel without safety seats for children, only when accompanying on adult's lap.