People with an IQ of less than 70 are also considered retarded. Another mental disorder is attention-deficit hyperactivity disorder. In this disorder people have an inappropriate lack of attention, are very impulsive, hyperactive, and then have difficulty organizing and completing work. The last common childhood disorder are anxiety disorders. In childhood anxiety, the patient has a fear of leaving home or their parents, avoid all strangers, and basically have excessive, un-called for worrying and fearful behavior.
Anxiety is fearful anticipation of coming danger, when there is nothing to trigger the fear.
A chronic disorder, there is no proven theory to the cause of all anxiety, but there is one kind of anxiety to which most people have suffered, where the cause is known. Let's say that you were riding your bike, then the wheel slipped on a rock and you fell down. The next time you ride your bike past the spot where you fell, you might be anxious, having an uncomfortable fear of danger that will happen. Psychiatrists have found that anxiety can be caused when a bad experience happened that involved a previously neutral object, or place. Thus you associate the pain you got from falling down, with the spot where you fell.