Thickened liquids are a common treatment for dysphagia; however, little is known about their effects in children. The aim of this systematic review was to summarize the state and quality of evidence for the use of thickened liquids on swallowing physiology, oral feeding, weight gain/growth, hydration, and pulmonary health outcomes in children with dysphagia. Another aim was to identify any increased occurrence of adverse effects that may be associated with their use in all children, not just those with dysphagia. A total of 24 electronic databases were systematically searched. Articles meeting the inclusion criteria were evaluated for methodological quality by 2 reviewers and vetted by a third. In total, 22 studies were included. Six studies, with significant methodological limitations, examined the effects of thickened liquids on swallowing physiology or pulmonary health outcomes and reported mixed findings. Sixteen studies examined adverse effects and indicated that among a select pediatric population with gastroesophageal reflux, no significant increase in the rate of adverse effects from the use of thickened liquids was noted. Results of this review highlight the insufficient evidence base for this popular treatment option. Additional experimental research is warranted to understand the efficacy and effectiveness of thickened liquid use in the pediatric population.