Dengue is a potentially life-threatening illness, and children are at higher risk of severity. This review aimed to systematize the identified clinical and laboratory parameters associated with severe dengue in children, as monitoring these signs and fluid-replacement therapy are actually the cornerstones of dengue treatment. Of the 527 studies initially reviewed, 21 were selected as follows: three cohort studies, three case-control studies, 14 cross-sectional studies and one not defined. Eighteen studies were carried out in Asia and three in the Americas. Hepatomegaly, lethargy, abdominal pain, bleeding, hemoconcentration and thrombocytopenia, all referenced as warning signs in the WHO 2009 Guidelines, were the clinical and laboratory parameters independently associated with severity in more than one study. The recognition of these known warning signs associated to severe dengue disease underlines the usefulness of the WHO 2009 classification.