On Russian material we traced dynamics of the acoustic characteristics of vowels and vowel sounds of the words 115 children aged 3 months to 7 years. There was a significant reduction in the duration and frequency values of the pitch vowels to 7 years of age children. We are the first to show that to 7 years relevant forms for Russian language sign the stressed vowel — long duration of the stressed vowel compared to unstressed vowel. Articulation of vowels is not fully formed. Data presented in this paper on the dynamics of the duration and frequency characteristics of vowels, on the one hand confirm the general laws of formation acoustic aspects of speech in ontogenesis. On the other — are original, as they reflect the assimilation of child articulations implemented in the Russian language.