Background/Objectives: Socioeconomic status and parental lifestyle influence dietary behaviors, including the administration of oral dietary supplements in children. The aim of this study was to evaluate the effects of selected health, dietary, and sociodemographic factors on the use of dietary supplements by children. Methods: In this cross-sectional observational study, a diagnostic survey based on the computer-assisted web interview method was conducted in November 2022 among 2826 parents whose children attend public educational institutions in Krakow, Poland. The study group included data on 497 nursery children (17.6%), 599 kindergarten children (21.2%), 1594 primary school children (56.4%), and 136 secondary school children (4.8%). Results: Among all respondents, 72.2% were taking oral nutritional supplements, with vitamin D supplementation being particularly popular in all groups. Logistic regression analysis identified predictors of supplement use, including special diet (p < 0.001), use of medication for chronic disease (p = 0.012), regularity of main meals (p = 0.022), and attending a sports school (p = 0.021). A decrease in supplement use was observed with the increasing level of education of children (p < 0.001). Conclusions: These results highlight the importance of various health, dietary, and sociodemographic factors in influencing decisions regarding dietary supplementation in children. Further assessment of dietary supplement usage should be conducted alongside evaluations of nutrient intake from the children’s diet.