Background Cognitive dysfunction is a common finding in individuals with multiple sclerosis at all ages. Cognitive impairment may drastically affect the life of younger patients with multiple sclerosis who are still undergoing education and schooling. Methods We carried out a systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses recommendations to assess the published data on multiple sclerosis and cognition in pediatric or juvenile patients. Only articles presenting original data on patients with multiple sclerosis diagnosed before age 18 years of age were included. Results Thirty-two articles fulfilled the inclusion criteria for this systematic review. The conclusion from all articles was that cognitive dysfunction in multiple sclerosis starting before the age of 18 years is both significant and disruptive and must be routinely assessed. However, assessment methods were heterogeneous and often very expensive to perform, whereas proposals for treatment were virtually absent in the literature. Conclusion Cognitive dysfunction can be a significant symptom of multiple sclerosis of early onset, but its impact and management needs to be better assessed. A task force should be created to study and manage cognitive dysfunction in pediatric and juvenile multiple sclerosis.