The article analyses theoretical approaches and empirical research of the influence of the children’s birth order in the family on their intellectual and creative abilities, achievements in education, personality traits, behaviors and social preferences. It is shown that the results of the studies vary depending on the method of data analysis - the effect of decreasing intelligence while increasing the birth sequence number detected when comparing indicators of large numbers of children with different birth order from different families, and generally not detectable in intra-family analysis data. To explain the differences obtained the authors used three basic theoretical models: a model of merge, the model of resource depletion and impurity model. Due to differences in birth order personality traits have more pronounced differences in the cognitive sphere. Research confirms that according to the results of the personal questionnaire «Big five» firstborns display more pronounced «honesty», and younger children-«kindness» and «openness» to experience. Individual work on features of social interaction of senior and subsequent children demonstrated a great ability of younger children to cooperation. Despite the fact that the prognostic significance of identified effects in large samples is not as great as in individual families, results may have practical significance for the pedagogical and psychological work with children.