You must contact the airline directly before purchasing a ticket for an unaccompanied minor. Most airlines allow unaccompanied minors to travel on their flights, but have special restrictions, so please check with the airline to confirm specific policies. Age restrictions vary by airline. In general, children under the age of 5 may never travel alone. Most airlines require unaccompanied minors services for children ages 5-14, and some require it through age 17. Additional fees apply (approximately $25-100 each way) and can be paid at check-in. For security reasons, most airlines do not allow unaccompanied minors to travel on the last connecting flight of the day. Some carriers require unaccompanied minors to travel on non-stop flights only. The specific flights required vary by airline, so check directly with them prior to making a reservation.
If you are traveling with an infant (a child less than 24 months old) in lap there is usually no charge for US travel. However, the airline may charge a special fare for International travel. Please check with airline(s) for specific rules for purchasing a ticket for an infant, as well as any documentation that may be required (such as a birth certificate).