As Delta Airlines states, all infants and children under two years old can travel on an adult's lap for free, without any restrictions. Parents can also purchase a ticket & use their specific child restraint system on the aircraft in an FAA-approved car seat or CARES harness on most flights. However, according to the FAA and the AAP, the safety experts strongly encourage parents to use child safety car seats or other child restraint systems when flying with their babies or other young children. Although not demanding, the use of car seats is always a big plus for everyone's safety.