Usually, by the time that your child reaches the age of 12 or 13, he or she could be babysitting for other children, but this is on condition that your offspring has the maturity to be able to handle any emergencies that come up and demonstrates the responsibility necessary to watch younger children. Most experts agree that teenagers do not need babysitters of their own, unless they're mentally or developmentally challenged.
On the other hand, you certainly should not leave your teenagers alone over the weekend without adult supervision and you shouldn't leave them to their own devices for hours on end, as law enforcement officers notice a sharp spike in criminal activity between the hours of 3:00 pm and 6:00 pm when teenagers are left on their own. If your job keeps you away from home in the afternoons on a daily basis and you're afraid that your teen may be filling his or her time with activities you don't approve of, you can have an older, more responsible teen come in, telling your teens that you totally trust them, but you know that their younger sibling is a real handful and the babysitter's there to watch the sibling, answer important phone calls that you don't want to trouble your teen to answer, show them some cool study tips that make homework go faster, help with household chores, etc.
Solutions to keeping teenagers occupied include after-school employment, supervised sports, or extracurricular courses in areas in which they've expressed an interest (hairstyling, car repair, Web design and so on). While you don't want to hover over your teenagers, you need to know where they are, who they're with, and that they'll be home by a predetermined time. If your teen is drawn to experimenting with drugs or alcohol, shoplifting, hanging out with gangs, or other self-destructive or criminal behavior, consider professional guidance.