This crazy out of control kid thing is an increasing worldwide phenomenon. Some kids have been successfully calmed by removing foods with colours and preservatives... even in bread, which was found to be the culprit in some.
While i also believe there are soulless automatons among us, there are also, according to some metaphysical writers of the 1900s many very laggard old souls incarnating on earth. I suppose you could speculate that some of these souls have been severely disturbed in past lives and are reincarnating with the same tendencies.
This would present the parents with a severe challenge. Also, in cases where food and current environmental influences can be ruled out, these extremely difficult relationships usually have their origins in past karma between parent and child [and siblings.] This karma might also include a demon possession dimension to it as a result of the dabbling in or the use of black magic.
Something may have gone drastically wrong in past life relationships. Karma can be very limiting to those involved and binds people together to balance the wrongs of the past. Those wrongs could have involved any of the things that humans are capable of doing to each other. Open any history book and chances are we are reading the stories of our own lives.
It's also possible that a parent may have volunteered at inner levels to assist a soul with severe issues of emotional instability. It's not always easy to judge the causes by an outer observation of the problem.
2 great reads on this subject are:
" Edgar Cayce on Reincarnation." by : Noel Langley and Hugh Lynn Cayce
" Life before Life" by : Dr Helen Wambach
edited to add Noel Langley as author of above book