The article features the speech genre “a message in a postcard” in Russian communicative practice of two periods: the period before 1917 Revolution and the Soviet period. The research is based on a subcorpus of 253 postcards written by children from the collection of postcards digital corpus “I am writing to you”. By observing the mastery of the genre canon by non-adult native speakers, we consider both the specifics of the speech genre and the dynamics of its changes that occurred at the turning point of two periods.