A study of acoustic characteristics of mother's speech directed to infants during the second half of they first year of life and to adults was carried out. The differences in the temporal structure of mother's utterances addressed to children of 12 month of age and utterances addressed to adults were shown. The decrease of quantity of key words in mother's speech addressed to children of the second half of the first year was revealed vs. speech addressed to children of the first half of first year. Spectral and temporal characteristics of stress vowels from key words versus functional words in mother's speech directed to children of the mentioned age were different. The differences in stressed vowels parameters of key words from the speech addressed to a children and from functional words from adult addressed speech were revealed. It was concluded that mother's speech addressed to children during the second part of the first year has the learning function and reports the information about syntax and phonology of native language.