Aproximatly 5% of all schoolkids has ADHD in one form or another and it stands for Attention Deficit Hyperactivity Disorder (over the years it has also been called MBD, ADD and MPH). In the american psyciatric manual released in 1994 ADHD has the following description:
-They who has clear attention problems
-They who has clear impulsive/hyperactivity problems
-And those who have a combination of the other 2

There is a subversion of ADHD called DCD (Developmental Coordination Disorder) but in the nordic regions its wrongly called DAMP (Deficits in Attention, Motor control and Perception) and this variation has the latter defentions as well as problems with controling your own body (Motor control).

Childs with this syndrome needs understanding from the enviroment as they usually are hyperactive they tend to get into trouble without understanding but note that they are not agressive or especially dangerous, they are just "overstimulated".

"ADHD, Tic Disorder, Tourette's Syndrome, and Obsessive-Compulsive Disorder are all characterised by an impairment of executive functioning and often occur together. There are thus indications of a similar neurobiological basis. This review presents an overview of neuroimaging studies of these disorders in childhood and adolescence, focusing thereby on magnet resonance imaging data. Studies provide concurring data about structural changes in the basal ganglia and the prefrontal cortex, and abnormal activation in the fronto-striatal circuitry in patients as compared to healthy controls. ADHD and Tourette's Syndrome are both associated with prefrontal aberrations. However, variances in Tourette's Syndrome are less pronounced, which might be due to compensation mechanisms. ADHD children show small, but more global, morphological alterations in the cortex and cerebellum, while Tourette's Syndrome seems to be linked additionally to differences in the occipital cortex. Furthermore, structural and functional data for obsessive-compulsive disorder indicate aberrations in the amygdala and thalamus, and functional changes in the orbito-frontal cortex. By comparison, findings in children with ADHD point towards abnormal activity in the ventral prefrontal cortex. To summarise, the data display an impairment of cortico-striato-thalamic circuits which appears to be associated with dysfunctioning motor inhibition, and impulsive behaviour and objectionable thoughts. Since the majority of the studies reviewed are characterised by small and heterogeneous samples, and since the studies differ in their methods, comparability is limited and general conclusions can not be drawn."

Source

This whole bunch of info tells us that ADHD children have changes in basal ganglia, prefrontal cortex as well as morphological changes (morph means visually change and it was more global and smaller then for the others who where limited to changes in basal ganglia and prefrontal cortex) in cortex and cerebellum. ADHD children also showed to have abnormal activity in the ventral prefrontal cortex.