The purpose of this investigation is to examine the process of acoustic features of vowels from child speech approaching corresponding values in the normal Russian adult speech. The vowels formants structure, pitch and vowels duration were examined. Word stress and palatal context influence on the formants structure of the vowels were taken into account. It was shown that the word stress is formed by 6 -7 years of age on the basis of the feature typical for Russian language. Formant structure of Russian vowels /u/ and /i/ is not formed by the age of 7 years. Native speakers recognize the meaning of 57-93% words in speech of 6 and 7-years-old children.