Adding a child to an existing British Airways booking is possible but cannot usually be done through the "Manage My Booking" portal on the website; you must contact the British Airways call center directly. If you are adding an infant (under 2 years old) who will sit on your lap, the airline will charge a percentage of the adult fare (typically 10%) plus taxes. If the child is older or requires their own seat, the process is more complex. Because BA's system generally doesn't allow "adding" a passenger to a confirmed PNR (Passenger Name Record), they usually have to create a separate booking for the child. Once the second booking is made, the agent will "link" the two reservations via a "TCP" (To Be Combined With) remark in the system. This ensures that in the event of a flight delay or rescheduling, the family is treated as a single unit. Be aware that if the flight is already near capacity, there may not be seats available to add a child, so it is always better to include them at the initial time of booking.