It depends upon the route. On all domestic routes, infants under 2 years can travel without a ticket on the adult’s lap. For Flights between the U.S., Canada, Mexico & the U.S. Virgin Islands, a Ticket is needed, but you only pay applicable taxes or 10% of the adult fare, plus applicable taxes (check fare rules). On the remaining international routes, a ticket is required and it costs a partial fare based on the destination.