Maternal infant-directed speech in Mandarin Chinese and Turkish (two mother–child dyads each; ages of children between 0;11 and 1;8) was examined to see if cues exist in input that might assist infantsʼ assignment of words to lexical and functional item categories. Distributional, phonological, and acoustic measures were analysed. In each language, lexical and functional items (i.e. syllabic morphemes) differed significantly on numerous measures. Despite differences in mean values between categories, distributions of values typically displayed substantial overlap. However, simulations with self-organizing neural networks supported the conclusion that although individual dimensions had low cue validity, in each language multidimensional constellations of presyntactic cues are sufficient to guide assignment of words to rudimentary grammatical categories.