This paper presents developmental data from 798 Chinese-speaking children aged three to six. An overall assessment of tone acquisition is reported with descriptive results from tone acceptability judgement, pitch contour type labeling and F0 slope patterns. The order of tone acquisition is Tone 4, Tone 1, Sandhi Tone 3, Tone 3, and Tone 2. High-register tones are generally acquired before low-register tones. Pitch contour types of perceptually acceptable tones primarily conform to phonologically predicted tone contours including Sandhi Tone 3. Unacceptable tones are actually more diverse. Based on the F0 property, the proportions of immediately erroneous slope patterns in Tone 2 are higher than in Sandhi Tone 3. As a whole, our developmental data consistently suggests that Tone 2, instead of Sandhi Tone 3, is the most challenging tone to acquire for Chinese-speaking children.