How does Virgin Blue, Polynesian Blue and Pacific Blue determine between an infant and a child?

Infants should be accompanied by an adult more than 15 years of age or more. An infant is a child from one day up to, but not including, two (2) years old and will travel free. It is not possible to purchase a ticket for an infant less than 2 years of age. The travelling parent or guardian of an infant must nurse the infant on their lap for take-off and landing and or when the seat belt sign is illuminated. A single adult cannot travel with two children under 2 years of age as each adult can only nurse one infant at any one time. Proof of age for any travelling infant must be carried at all times - birth certificate or passport will be accepted as form of identification (ID). In the instance when proof of ID cannot be provided when requested, airport staff may / can refuse boarding. Virgin Blue Boeing 737 aircraft are not fitted with bassinets, so all infants and children up to 2 years must be travelling with a guardian or parent (seated on the lap of the adult). A baby car seat will ...  more