If your kids are under 2 years old, then airlines call them an infant who is eligible to travel in flight in their parents lap. However, you can book Flight for an infant or child in many ways by calling or through the official website. To learn the booking process, read below.

Visit the official website of the airline.
Then click the flight or book option.
And share the flight information from the traveler and add an infant or child.
Enter your child or Infant information.
Lastly, pay the cost of the booking and then you receive an mail from the airline.

For more details, visit the Airlinesunaccompaniedminor website.
https://www.airlinesunaccompaniedminor.com/blog/book-flight-for-infant-or-child