Can the flight booking API book a ticket for a baby travelling on a parent's lap?

Yes, a flight booking API can usually book a baby who travels on a parent's lap, as long as the airline and the supplier behind that fare support it. The infant is sent with the search as a separate passenger type, so the fare that comes back already accounts for them rather than being worked out afterwards. You will normally need the baby's full name and date of birth at the time of booking, and a passport for international travel, because the airline checks the age against the travel date.

There are real limits worth knowing before you promise this to a customer. The airline decides the infant fare and the taxes that go with it, so it varies from one airline to another and it is not always a simple share of the adult fare. Some suppliers and some low cost carriers do not return infant pricing through the API at all, and those bookings have to be finished with the supplier or the airline directly. One adult can normally carry only one lap infant, and a baby who needs a seat of their own is booked as a child instead.

If the booking goes through, the airline usually issues the infant as its own ticket tied to the adult, and your software should show both on the same booking so your staff are not chasing two records. Remember too that a baby close to the airline's age limit on the way out may be over it by the return date, and the airline will treat that as a child fare.

Ask your supplier which of your airlines return infant pricing through the API on your plan, then run a live search with an infant before you advertise it, so you know what your staff will actually see.