Introduction: Vegetarian diet is increasingly used in both adults and children. Study aim: The aim of the study was to determine the differences in the body build and reaction time of vegetarian and non-vegetarian children on the background of socio-economic factors. Material and methods: The material consisted of 218 children, including 47 vegetarians (25 boys and 22 girls) and 171 non-vegetarians (93 boys and 78 girls) from 3 to 15 years. The research consisted of a survey and measurements. The survey included questions such as date of birth, child's birth parameters (length, weight, Apgar scores), child's diet (vegetarian/non-vegetarian), mother's diet during pregnancy (vegetarian/non-vegetarian), breastfeeding (yes/no), number of months of breastfeeding, mother's diet during lactation (vegetarian/non-vegetarian), maternal and parental education level (elementary / trade/ college / university), living conditions and the number of siblings. The height and body mass, skin-fat folds on the abdomen, shoulder and arm (sum of 3 skinfolds) were measured, BMI was calculated and the reaction time was assessed using the Quickstick ruler. The General Linear Model, Wald's test, U-Mann-Whitney test and Principal Components Analysis were applied. Results: The results showed that vegetarian children who came from families with a higher socio-economic status than non-vegetarian were significantly longer breastfed. The somatic build of vegetarian children, including height, BMI and the sum of three skinfolds significantly differed from non-vegetarian children. The vegetarian children were shorter, with lower BMI and lower sum of the three skinfolds, as well as their reaction time was longer. Conclusions: Vegetarian diet affects the height, BMI and body fatness, as well as the reaction time in children at the age of 3-15.