Who Should Get Background Checks and How Often?

My children's basketball coach, school teachers and room moms, and Sunday school teachers have had criminal background checks performed. But my daughter's cheerleading coaches haven't. Their babysitter hasn't either. I also learned that my children's family care provider only had one done 20 years ago. So, who should have a background check and how often? And, should I be worried if someone doesn't have one? Maybe. Or maybe not. Remember too that checks are not free, aren't always perfect, and come with no guarantees that they will keep the "bad guys" away from our precious kids--although I would like to believe that they certainly will help steer ones with records to another line of work!