We aimed to investigate whether nuclear factor kappa-B activation, as evaluated by gene expression of its inhibitor (I-κBα) and cytokine serum levels, was associated with myocardial dysfunction and mortality in children with septic shock. Twenty children with septic shock were prospectively enrolled and grouped according to ejection fraction (EF) <45% (group 1) or EF ≥45% (group 2) on the first day after admission to the pediatric intensive care unit. No interventions were made. In the first day, patients from group 1 (n = 6) exhibited significantly greater tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-10 plasma levels. However, I-κBα gene expression was not different in both groups. Mortality and number of complications were significantly greater in group 1. Patients who died had greater plasma concentrations of TNF-α. In conclusion, TNF-α and IL-10 are involved in myocardial dysfunction accompanying septic shock in children, and TNF-α is associated with mortality.