When traveling with your little one, you'll need to add them as a passenger on your UA ticket. Infants under the age of two can fly for free. You can/may choose to purchase a seat for your infant, which will allow them to have their own area and possibly a car seat. To add an infant, you'll need to reach out via their website You'll be required

Needing to update the passenger name on your United Airlines flight ticket can be a common occurrence. While it's best to get this sorted out ahead of time you depart, They do offer choices for making these changes. You might need to speak with United Airlines immediately. Be prepared to provide your booking reference number and other relevant info