Young Teen College Girls At Halloween Parties

The earliest known use in print of the term "trick or treat" appears in 1927, from Blackie, Alberta, Canada:
Hallowe'en provided an opportunity for real strenuous fun. No real damage was done except to the temper of some who had to hunt for wagon wheels, gates, wagons, barrels, etc., much of which decorated the front street. The youthful tormentors were at back door and front demanding edible plunder by the word “trick or treat” to which the inmates gladly responded and sent the robbers away rejoicing.
The thousands of Halloween postcards produced between the turn of the 20th century and the 1920s commonly show children but do not depict trick-or-treating. The editor of a collection of over 3,000 vintage Halloween postcards writes, "There are cards which mention the custom (of trick-or-treating) or show children in costumes at the doors, but as far as we can tell they were printed later than the 1920s and more than likely even the 1930s. Tricksters of various sorts are shown on the early postcards, but not the means of appeasing them". Trick-or-treating does not seem to have become a widespread practice until the 1930s, with the first U.S. appearances of the term in 1934, and the first use in a national publication occurring in 1939.