This study aims to assess the functional outcome of children treated with elastic stable intramedullary nailing (ESIN) for displaced proximal humerus fractures using the short version of the disabilities of the arm, shoulder, and hand outcome questionnaire (Quick DASH). Fifty-eight consecutive children with displaced proximal humerus fractures were treated with ESIN. Fifty-two children (89.7%) were available for follow-up and responded to the questionnaire after hardware removal. Average age at time of injury was 11.1 ± 2.8 years (range, 4-15.9). Among the 52 patients available for evaluation, 37 had a Quick DASH score of 0 (71.1%), seven a score of 2.3 (13.5%), four a score of 4.5 (7.7%), and four a score of 6.5 (7.7%). Shoulder and elbow ranges of motion were comparable with the noninjured side. No skin irritation or local infections were observed. There was no radiographic evidence of delayed union, refracture, hardware migration, or secondary displacement. Mean follow-up was 18.3 ± 8.3 months (range, 6-39.5). Our study reports good functional outcomes in children with closed isolated fractures, both physeal and metaphyseal, of the proximal humerus treated with ESIN. The use of a standardized rating scale is recommended to homogeneously compare functional outcome and may facilitate the comparison of clinical outcome in different patient populations.