The longitudinal study of mother speech interaction with 4-6-years-old dizygotic twins (n=5 triads) was performed. The characteristics of maternal speech addressed to twins, characteristics of children' speech development due to the order of the birth are investigated. The first-born child in pair have a higher level of speech development as compared to the second-born child by syntactic structure of sentences in dialogue, number of consonants, meanings of pitch in vowels. Correlation between characteristics of maternal speech and the level of twin's speech development is revealed. When mothers interact with the second-born twins they stimulate them to communication more then the first-born twins.