On the Delta.com, type "meal selections" and you will see information about meal options at "http://www.delta.com/content/www/en_US/traveling-with-us/onboard-experience/food-and-beverage/special-meals.html". Look at your child's itinerary on the "MyTrips" page, and scroll down and check the option for meal selection which you can select up to 24 hours in advance.