Purpose of Review <p>Gastrointestinal (GI) issues are common in children with attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD), and they can worsen behavioral symptoms. In order to find new therapeutic targets, this review compiled the primary symptoms and gastrointestinal abnormalities that affect individuals with ASD and ADHD, emphasizing physiopathology features.</p> Recent Findings <p>Eighty-nine articles met the inclusion criteria. Constipation, diarrhea, gastric reflux, abdominal pain, and abnormalities in digestive enzymes were more common in children with ASD. Meanwhile, constipation and fecal incontinence seem to be problems for those with ADHD. Furthermore, abnormalities in the pathways that link the gut-brain axis, such as dysbiosis and increased intestinal permeability, have been observed in both animal models and patients with neurodevelopmental disorders. These findings open a field to look for novel treatment targets and assist understand how the gastrointestinal tract influences the central nervous system in these people. Additionally, successful diagnosis and treatment of co-existing diseases affecting the GI tract in individuals with ASD and ADHD depend on the cooperation of neurologists, gastroenterologists, and other specialists.</p> Summary <p>Modifying the gut microbiota is a promising strategy given the data linking dysbiosis and leaky gut to gastrointestinal symptoms in ASD and ADHD. Finding products from this microbiota that support the function of the intestinal barrier and its targets, as well as strategies to preserve the integrity of the tight junction, can lead to new treatment options for gastrointestinal comorbidities in neurodevelopmental disorders, which will improve their neurological manifestations.</p>