When we talk about child protection issues, we see that there are high frequencies of mental disorders in children within that population. It is helpful to see the average rates of disorders in children as that gives us a base of comparison. In the USA, the National Institute of Mental Health has published data that helps us to see the "average" rate of mental health issues within the general population of children.
Describing this data, they state:
The Centers for Disease Control and Prevention's National Health and Nutrition Examination Survey (NHANES) includes prevalence data for children ages 8 to 15; a slightly younger age range than the data from the NCS-A chart above. These data show that approximately 13 percent of children ages 8 to 15 had a diagnosable mental disorder within the previous year. The most common disorder among this age group is attention-deficit/hyperactivity disorder (ADHD), which affects 8.5 percent of this population. This is followed by mood disorders broadly at 3.7 percent, and major depressive disorder specifically at 2.7 percent.