Although the idea of older children and teenagers spending time unsupervised is no longer novel, with as many as one third of the nation's school age children spending some time unsupervised in a typical week, there are valid safety concerns in leaving children at home alone.
You can check with your state's Department of Social Services to see if your state has a minimum age for leaving children unsupervised. You are likely to find that there is no specific age, although the common recommendation is that children under twelve be provided with appropriate supervision while their parents are away from home. There may also be a suggestion that an older sibling, even if old enough to be left at home alone, is not necessarily an appropriate babysitter for younger siblings.
There is good reason not to set a specific age at which children may be left at home alone. Specifically, no matter what age you pick there will be some children who are not sufficiently mature to look after themselves. It would not be good public policy to effectively grant parents immunity for the consequences of what they know to be poor parenting decisions, merely because a child has reached the age specified in a statute or regulation. Also, the nature and duration of the parents' absence can significantly affect the age at which the child should be left alone. A twelve-year-old may be perfectly comfortable taking care of himself after school until a parent gets home from work, but that does not mean that he's sufficiently mature to stay at home alone while his parents take a two-week tour of Europe.
When a parent leaves younger children home alone, the police or child protective services agencies are likely to respond to a tip, and verify that the children have appropriate adult supervision and aren't in any danger. With preteens and teens, the most likely reason for protective services or the police to learn that a child is home alone is an accident or other tragedy. The parent may then have to establish in retrospect why the children were left alone. It is best for parents to make these decisions with caution, to make sure that their children have appropriate maturity to be left alone, and to make sure that they are instructed on how to handle emergencies and have emergency contacts to assist them in case something goes wrong.
It may appear to some that the state should take a firmer stand on leaving children home alone. That it should set minimum ages and presumptions, with the goal of maximizing child safety. However, the effects of any such rules would fall disproportionately on working families, who may have their children spend a period of time alone before or after school, or on poor families who cannot afford child care. It would consume the limited resources of protective services agencies, pursuing cases involving children who really are sufficiently mature to look after themselves for limited periods of time, distracting them from focusing on cases of bona fide child neglect. Also, there's a question of how much government interference our society wishes to tolerate in parenting decisions.
The proper care and supervision of children, including preteens and teenagers, is a valid subject for child custody litigation. While courts are usually reluctant to put undue weight on a parent's need to use child care, the absence of any supervision is a more serious concern. Thus, when making a custody decision, a court may be inclined to consider a parent's ability and willingness to limit the amount of time the children will be left unsupervised. Parents should consider exploring the possibility of before- and after-school programs, some of which are available directly through the public schools, which may be available at a reasonable cost.