You may have had a psychotic break but maybe not. Children go through many emotional and psychological changes throughout their developing years. If you had a psychotic break, it would have been difficult to have been overlooked. Undoubtedly, someone would have noticed your odd behavior or thinking. It is possible that you had a psychotic break but unless you were evaluated and diagnosed, then it is difficult to know for certain.
To answer your questions, determining the cause of a psychotic episode is very difficult. Psychosis in children is rare but research shows that they can experience symptoms of psychotic disorders such as schizophrenia.
Generally speaking, there are multiple possible causes of psychosis in children that include: stress, environmental factors or genetic influences. Other possible causes of psychosis include organic or physical illnesses such as epilepsy or a brain tumor. Only a neurological or physical examination could have ruled out these latter possibilities.
The reality is, it will be difficult to know with certainty what could have caused a possible psychotic episode. Sometimes people display symptoms but do not necessarily meet the criteria for a specific disorder. The latest edition of the DSM-IV TR, the book mental health professionals use to diagnose mental health disorders, includes a specific disorder, diagnosable only in adults, called schizophreniform disorder. Schizophreniform disorder is basically when an individual has one schizophrenia episode but never has another. To the best of my knowledge, this particular disorder has not been investigated among children but research has shown that individuals who report psychotic symptoms as children may be at risk for developing schizophreniform disorder later in adulthood. It is important to keep in mind that even if you had a psychotic episode as a child, it does not mean that you will have another.
I hope this answers your questions. If you’re interested in learning more about this topic I would recommend your reading more about psychosis in children.