When I was at school I am sure I remembered the teachers explaining about Halloween. If I remember correctly it was a festival or celebration for Celts and Druids or Priests called Samhain.
November the 1st, was called the feast of Samhain. The night before or ‘eve’ of Samhain was believed to be the night when evil spirits would return to earth and inhabit the living souls of animals or even the Celts themselves ! Thus the Celts would put on costumes as a disguise to confuse the evil spirits. Hence our tradition today of dressing up at Halloween.
I am sure the origins of Halloween are more complex than my explanation, but it has always been one of my favourite time of year. To be enjoyed whether young or old !