Japanese polite language (teineigo) varies with the speaker-addressee relationship as well as social norms. Descriptive studies have found that young Japanese children use polite-speech early in development. This claim was experimentally tested in 3- to 6-year-old Japanese children and correct use of polite verb forms was found even in the youngest children. The early acquisition of these verb forms is surprising, because parental speech to children is mostly not polite, so it is not clear how children acquire the knowledge of how to use polite forms. To examine this, a large scale corpus analysis of polite language was performed using a probabilistic measure of intended addressee. We confirmed that parental speech is mostly not polite, but parents also produced a substantial amount of polite language that varied appropriately with addressees and this can help to explain the early use of polite speech in Japanese children under experimental conditions The paper is an Rmarkdown script with the experiment and corpus stats within, so the files that are needed to run it are provided in the rmdfiles folder. 1. Experiment data ExpTeineigoClean.xlsx 2. Verb Corpus data rolesJAUtt2019-04-19.rds14.5 3. Noun Corpus data nounJAUtt2019-04-19.rds11.7, longnounJAUtt2019-04-19.rds28.6