This study investigates the acoustic correlates of contrastive word stress in bisyllabic and trisyllabic German words, produced by children and their parents. Results of the acoustic analysis of speech data are reported that were collected from three children aged 2;3 to 6;1 and their mothers during a period of two years, as a part of a more comprehensive study on the acquisition of word stress in German. Whereas recent findings suggest that infants show an early perceptual preference for rhythmic patterns of their native language, contrastive stress is supposed to be acquired relatively late. The results of the study presented here suggest that German children between 2 and 6 years of age are able to produce contrastive word stress but differ in their choice and usage of the parameters that mark stress. We found that, for German, vowel duration is the most reliable correlate of word stress in the utterances produced by all three children as well as their mothers. Adult-like usage of fundamental frequency, intensity, and several voice quality parameters appears to be acquired later than that of duration; this observation may be confounded by the finding that these parameters appear to be used less consistently than duration to mark stress even by the mothers.