In an early part of the story, Kipling uses dialect to emphasize Michael's young age and to endear the character to the reader. Helen reproduces his childish manner of speaking, which emphasizes their playful mother-son rapport and shows that she is capable of speaking his language.
At six, he wished to know why he could not call her ‘Mummy’, as other boys called their mothers. She explained that she was only his auntie, and that aunties were not quite the same as mummies, but that, if it gave him pleasure, he might call her ‘Mummy’ at bedtime, for a pet-name between themselves.
In this passage, the narrator uses two sets of diction to reproduce the conversation between Helen and Michael. Placing the words "Mummy" and "mothers" side by side creates an endearing contrast, and shows that Helen toggles between speaking Michael's language and speaking the language of adults. This is also shown through the word "auntie," which Helen uses in place of the word "aunt."
Ultimately, despite being carried out through simple and childish diction, the conversation they are in the midst of having is quite complex. Michael does not yet understand all the nuances of why Helen is sensitive to being called "Mummy," but the secrecy involved in their resolution to the problem makes him understand that there is something sensitive and unusual about their relationship—not to mention the way their relationship is perceived by others.
Kipling again employs dialect when recounting a subsequent argument between Helen and Michael, after he discovers that she has told her friends that he calls her Mummy at bedtime. After she, rather contradictorily, justifies her act with the line that "it's always best to tell the truth," he articulates an insightful, though not terribly eloquent, retort:
All right, but when the troof’s ugly I don’t think it’s nice.
Like many young children, Michael is still unable to pronounce the th-sound in "truth." The alternate spelling, "troof," reinforces his childish dialect all while showing that he is clever for his age. Another instance in this conversation that underlines his precocity is the grammar of his statement "You've hurted me in my insides." A rather poetic description of the physical sensation that often accompanies disappointment and sorrow, this sentence adds to Michael's characterization and the reader's attachment to the young boy.