According to DOT regulations, kids under the age of 2 can sit on the parent's lap. Therefore if you are traveling with a child under the age of 2, you do not need to purchase a ticket for them if you choose to have them sit on your lap. If you wish to bring a car seat on the bus, you will need to purchase an extra seat for the child to ensure seat is reserved and available for the car seat and child. Kids  years or older must be seated in their own seat and a ticket must be purchased for them.