According to the U.S. Travel Association, about 30 percent of leisure travelers are families traveling with children (or grandchildren), and they go on an average of 4.5 trips per year. The total number of children who travel solo, however, isn't readily tracked but some airlines give estimates. For example, an estimated 200,000 unaccompanied minors -- kids without their parents or guardians -- fly with American Airlines every year.
These kids are usually between the ages of five and 14 (although this varies). Unaccompanied minors may or may not be required to show photo identification, and even if it's not a requirement (some airlines require ID, some don't), it's a good idea to send kids traveling with IDs that include emergency contact information.