Autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) are neurodevelopmental disorders which occur in childhood and may persist into adulthood. Although the etiology of these disorders is largely unknown, genetic and environmental factors are thought to play a role in the development of ASD and ADHD. Allergic immune reactions, in prenatal and postnatal phases, are examples of these environmental factors, and adverse reactions to foods are reported in these children. In this review, we address the clinical and preclinical findings of (food) allergy in ASD and ADHD and suggest possible underlying mechanisms. Furthermore, opportunities for nutritional interventions in neurodevelopmental disorders are provided.