The aim of this study was to evaluate the rate of open reduction and complications of elastic stable intramedullary nailing (ESIN) in treating unstable diaphyseal forearm fractures in children. We performed a retrospective review of a consecutive series of 102 paediatric patients with a mean age of 9 years (range: 7–14 years) who underwent ESIN of unstable closed forearm fractures at three different centres. Closed reduction of one or both bones was achieved in 68 (67%) patients and open reduction was required in 34 (33%) patients. The rate of open reduction in single-bone fractures (52.2%) was significantly higher than that in both-bone fractures (27.8%) (P=0.04, Fisher’s exact test). All the fractures united within 3 months. There were six refractures following nail removal. Five patients had superficial wound infections. Seven patients developed neuropraxia of the sensory branch of the radial nerve. All resolved spontaneously within 3 months of the surgery. ESIN is an effective technique in treating unstable diaphyseal forearm fractures. The need for open reduction should be decided promptly following failed attempts of closed reduction. Single-bone fractures are more likely to require open reduction than both-bone fractures. The radius should be reduced and stabilized first. If open reduction is required, this should be performed through a volar approach rather than a dorsal one.