This article reports on new data on the association of breastfeeding with DNA methylation in the peripheral blood cells of 37 children aged from 9 months to four years. Whole-genome DNA methylation profiling was performed using the Illumina Methylation EPIC array. The Epigenome-Wide Association Study (EWAS) revealed an association between the duration of breastfeeding and the methylation level of 4276 CpG sites related to 2635 genes. According to the functional annotation, these genes were predominantly involved in the control of cell signaling systems, the development of anatomical structures and cells, and, above all, were related to the development and function of the immune system and the CNS. The results of the study allowed assuming a special role of the oxytocin signaling pathway, as a potential trigger of coordinated epigenetic changes in the genes involved in the CNS function in response to breastfeeding.