Basically, if your child is age seven or younger, they should never be left alone. Kids ages 8-10 can be alone briefly, and ages 10-13 for longer periods, provided there is back-up supervision. Babysitters should be at least 12-13 years old, and can babysit for longer periods as they grow older.Again, this is a very individual decision, and these ages are only general guidelines. You need to decide if your child is mature enough.asically, if your child is age seven or younger, they should never be left alone. Kids ages 8-10 can be alone briefly, and ages 10-13 for longer periods, provided there is back-up supervision. Babysitters should be at least 12-13 years old, and can babysit for longer periods as they grow older.