ADHD in children is a common behavioral abnormality problem. ADHD in 3-year-old children may show symptoms such as non-stop dancing of the hands and feet, inability to sit quietly, inability to concentrate, and emotional instability. If your child has symptoms similar to ADHD, you can further do the hand-turning test, which is to have your child’s four fingers together and thumbs in the palm, repeatedly turn both hands, observe the amplitude of the elbow swing, the degree of the child’s fingers together and the time it takes to keep them together, which can determine the degree of flexibility of your child’s hands. You can also do the nose pinch test, by having the child open and close his eyes and repeatedly point to the tip of his nose, to determine whether the child’s movements are too clumsy, or you can check the brain waves through an electroencephalogram to see if there are any abnormalities.