Final answer:
Children under the age of 2 who are traveling with an adult on an airplane are generally considered lap infants and do not need a separate ticket. However, it's important to check the airline's policies.
Step-by-step explanation:
When traveling with an infant, whether they need a ticket or not depends on the airline and the age of the child. Generally, children under the age of 2 are considered lap infants and do not require a separate ticket. Instead, they can sit on the lap of an adult during the flight. However, it is important to check with the specific airline's policies as some may require you to purchase a ticket for the infant.