The anthropocentric focus of contemporary linguistic research highlights the specificity of individual linguistic worldview which includes a personal sense of toponymy. The studies discussing the ways that toponymic concepts are apprehended, memorized, and retrieved from memory are usually based on experimental data. But looking at irregular changes that toponyms may receive in individual speech is no less informative. Children’s speech proves the most valuable source for this, since it is less bound to the language norms of everyday communication, which makes the modifications more distinct. The author uses a collection (more than 170 items) of St.-Petersburg toponym modifications from children of 3–11 years old, drawing some conclusions about the peculiarities of their auditory perception (the role of individual frequency, phonemic and supra-phonemic word features in building semantic awareness, the specificity of phoneme patterns recognition by children and the processes of etymologizing and rethinking the internal form of the word), memorizing and storing information (the study of the child’s vocabulary connections and semantization of words including proper and common nouns; making up words and grammatical forms in the course of their multiple reproduction). Analysis of this real-life data brings clarity over some structural and functional aspects of individual linguistic systems and their speech manifestations. The information obtained can be used for creating child’s speech, memory, and attention training programs, as well as for studies in local history.