This paper contributes to the ongoing debate on how much detail young children's word representations contain. We investigate early representations of place of articulation and voicing contrasts, inspired by previously attested asymmetrical patterns in children's early word productions. We tested Dutch-learning 20- and 24-month-olds’ perception of these fundamentally different contrasts in a mispronunciation-detection paradigm. Our results show that different kinds and directions of phonological changes yield different effects. Both 20- and 24-month-olds noticed coronal mispronunciations of labials, but not vice versa. The 24-month-olds noticed voiced mispronunciations of voiceless stops, but not vice versa, while the 20-month-olds failed to notice any voicing mispronunciations. We argue that early lexical representations are specified in very systematic ways, that not all phonological contrasts are encoded at the same time and that the phonological system of a language determines which contrasts are specified first in the representations of early words.