Abstract Background Malnutrition in childhood has lasting consequences; its effects not only last a lifetime but are also passed down from generation to generation such as short stature, school-aged children are the most vulnerable section of the population and require special attention, including nutrition. Method We searched Medline through PubMed, Scopus, and Web of Science to identify all observational studies published before Jun 2022. Observational studies with a pediatric population aged 5–18 years that evaluated risk estimate with 95% confidence intervals the relationship between dietary diversity and undernutrition (wasting, stunting, and thinness) were included. The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) were followed. Results This is a first systematic review and meta-analysis with a total of 20 studies were eligible (n = 18 388). Fourteen data evaluated stunting resulting in a pooled effect size estimated odds ratio of 1.43 (95% CI: 1.08–1.89; p = 0.013). Ten data evaluated Thinness resulting in a pooled effect size estimated odds ratio of 1.10 (95% CI: 0.81–1.49; P = 0.542). Two studies were revealed wasting with a odds ratio of 2.18 (95% CI: 1.41–3.36; p-value