According to Delta Air Lines, a little passenger, who is under 2, can travel on their parent's lap and can travel on domestic (free) and international (10% of adult fare) flights. Additionally, diaper bags are considered an essential item for the infant; hence, they are allowed on the flight. On an international flight, the infant is allowed to take a 20 lb weight bag with them.

Source: https://www.airlinesunaccompaniedminor.com/blog/delta-airlines-infant-policy