Yes, infants (below 24 months old) need to be booked a flight ticket. This ticket should be booked from your agent if you need a SEAT for your infant. In that case, you will have to pay a child fare. This fare can be more/less than 70% of adult fare + taxes. However, if you do not need a seat for the baby and will prefer to carry her/him in your laps, you may pay  infant fare (around more/less 10% of adult fare + taxes) either at the airport or at the time of reservation.