Aim: The aim of this review was to determine the effectiveness of hand splinting for improving hand function in children with cerebral palsy (CP) and brain injury. Method: A systematic review with meta-analyses was conducted. Only randomized and quasi-randomized controlled trials in which all participants were children aged 0 to 18 years with CP or brain injury and a hand splint (cast, brace, or orthosis) were included. Results: Six studies met the inclusion criteria. No study included participants with a brain injury; therefore, the results relate only to CP. Five studies investigated 'non-functional hand splints' and one investigated a 'functional hand splint'. Moderate-quality evidence indicated a small benefit of non-functional hand splints plus therapy on upper limb skills over therapy alone (standard mean difference [SMD]=0.81, 95% confidence interval [CI]=0.03-1.58), although benefits were diminished 2 to 3 months after splint wearing stopped (SMD=0.35, CI -0.06 to 0.77). Interpretation: In children with CP, hand splints may have a small benefit for upper limb skills. However, results are diminished after splint wearing stops. Given the costs - potential negative cosmesis and discomfort for the child - clinicians must consider whether hand splinting is clinically worthwhile. Further methodologically sound research regarding hand splinting combined with evidence-based therapy is needed to investigate whether the small clinical effect is meaningful.