Health professionals are reluctant to diagnose children with personality disorders because they don't want to "label" them. These labels could become a self-fulfilling prophecy. In addition, children change so much from month to month and year to year that tests that show a particular tendency at one time may change drastically in a few months.
Half the battle in life is the lens through which a person views themself. Think about it. If someone tells you that you are the greatest, smartest, bestest, fastest yadayada. Soon you will come to believe you can do anything. If people are telling you that you have something wrong with you, then you will begin to think that you are not good enough. Plus, health professionals are just people like you and me. They do not have all the answers and can be wrong at times. Just think of all the "disorders" someone can diagnose on you. It would be best not to listen to what anyone tells you about yourself.
There are at least ten different personality disorders. To diagnose any one of them:
1. there must be pervasive behavior that deviates from one's culture,
2. it must occur across a broad range of personal and social situations,
3. this enduring pattern of behavior must lead to significant personal distress or impairment in important areas of functioning,
4. and you have ruled out physiological causes or other mental disorders.
These criteria are paraphrased from the DSM-IV, Diagnostic and Statistical Manual-IV of the American Psychiatric Association, 1994.
As Ms. Sue has indicated, with the variability of childhood behavior, it would be very unlikely to find behavior fitting these criteria for any particular personality disorder in children.
I hope this helps. Thanks for asking.