Oxidative stress is a condition determined by an imbalance between antioxidant and oxidative factors. Oxidative stress can have serious consequences on our organism. Indeed, it causes both necrosis and cell apoptosis, determining cellular aging, increased carcinogenesis, vascular stiffening, increased autoimmune diseases, and muscle decay. In the context of pediatric syndromes, oxidative stress could play a role in the first order. In fact, our review of the literature showed that in some pathologies, such as fetal alcohol spectrum disorders, oxidative stress related to the intake of ethanol during pregnancy is a main etiological factor determining the associated clinical syndrome. On the contrary, in Williams syndrome, Down syndrome, Marfan syndrome, Gaucher syndrome, ataxia-telangiectasia, autistic spectrum disorder, Fanconi’s anemia, and primitive immunodeficiencies, the increase in oxidative stress is directly associated with the genetic alterations that cause the same pathologies. Although further studies are needed to better understand the relationship between oxidative stress and pediatric diseases, a better knowledge of this crucial issue encourages future therapeutic strategies.