Listeners often misperceive speech contexts that contain unattested, ill-formed phonological sequences and repair them to create well-formed or close-to-native sequences. However, what guides the misperception and repair processes still has to be studied in depth. In the present study, French adults and typically-developing children were presented aurally with monosyllabic pseudowords and their disyllabic /u/-inserted counterparts, with the well-formedness of the latters' onset clusters being manipulated (e.g., Bbal/ vs. /gmal/). Here, we showed that onset clusters are increasingly misperceived as universal sonority-related markedness increases, i.e., from the most well-formed through to the most ill-formed onset clusters (e.g., /gm/-> /bd ->/b/). A posteriori measurements confirmed that the misidentification is due to a phonological repair during which an illusory epenthetic /e/-like vowel, i.e., a prototypical vowel inserted in French (e.g., /b/), is inserted in order to restore an attested phonological CV syllable structure. But these patterns are not primarily affected by acoustic-phonetic cues or sonority-unrelated cues. Moreover, both sensitivity to universal sonority-related markedness and epenthetic repair were found to be available at an early age in children. These results strengthen the hypothesis that acoustic-phonetic cues and language-specific properties, such as statistical properties for example, are not solely responsible for speech perception.