While many kids dress up every year to trick or treat, the origins date back to England and Ireland in the middle ages. It's similar to the old practice of souling. People would go door to door on Hallowmas (Nov 1) to receive food in exchange for prayers for the deceased on All Souls Day (Nov 2) the next morning.
Also this is me when I was 2 or 3 before we went trick or treating. I was the bear, I seriously don't know why I picked that off all costumes. My oldest brother was a hobo. It was a stupid costume but a cool mask. My 2nd oldest brother was Batman. My 3rd oldest brother was Leonardo from the Ninja Turtles. I would wear the same costume a few years later.