Yes, traveling companions fall under three categories:
Personal Care Attendant
A personal care attendant (PCA) is an individual who must accompany a passenger in order for the passenger to fulfill the purpose of his or her trip. For an individual to qualify as an attendant, the ADA-certified passenger must have established the need for a PCA during the ADA eligibility process. PCAs are always allowed to ride with an eligible passenger and are not required to pay a fare. They must, however, travel from the same point of origin and to the same destination as the passenger.
Companion
A companion is someone riding with an ADA-certified passenger, but not as a PCA. One companion is always allowed to ride with the passenger as long as a reservation has been made for the companion, and the companion travels from the same point of origin to the same destination. The companion pays the same fare as the passenger. More than one companion is allowed if space is available.
Children
Passengers traveling with children under the age of five are responsible for providing an infant car seat.