Physical activity is promoted for optimal health but may carry risks for children who require medically necessary activity restrictions. The sensitivity, specificity, and reliability of the Get Active Questionnaire (GAQ) for identifying children needing special considerations during physical activity was evaluated among parents of 207 children aged 3 to 14 years (97 (47%) female, mean age of 8.4 ± 3.7 years). GAQ responses were compared with reports obtained directly from the treating physician (n = 192/207) and information in the medical chart (clinic notes/physician letter, n = 111/207). Parent GAQ responses (either “No to all questions” or “Yes to 1 or more questions”) agreed with physician (κ = 0.16, p = 0.003) and medical record (κ = 0.15, p = 0.003) reports regarding the need for special consideration during physical activity (Yes/No). Sensitivity was 71% (20/28) and specificity was 59% (96/164), with few false-negative responses. The GAQ was most effective for rheumatology and cardiology patients. False positives were 29% to 46%, except among chronic pain (80%) and rehabilitation (75%) patients. Test–retest reliability was moderate (Cronbach’s α = 0.70) among 57 parents who repeated the GAQ 1 week later. The GAQ effectively identified children not requiring physical activity restrictions and those with medical conditions similar to those of concern among adults. Additional questions from a qualified exercise professional, as recommended for a “Yes” response on the GAQ, should reduce the false-positive burden. Indicating the timeframe of reference for each question and including an option to describe other special considerations (e.g., medication, supervision) are recommended.