Some airlines accept unaccompanied children aged 5 to 11 years and will escort them from check-in through to their arrival at the destination airport (usually for a fee). Be sure to consult your airline's terms and conditions before booking a flight for an unaccompanied minor.
For international travel, airlines must establish a policy for unaccompanied minors and prohibit minors under the age of five from travelling without their parent or an accompanying person who is at least 16 years old.
Reference: Airline obligations in this area are listed in their tariffs. Specific obligations for international travel are set out in the Air Transportation Regulations.