OBJECTIVE To quantify age-related variability of insulin needs during day and night closed-loop insulin delivery. RESEARCH DESIGN AND METHODS We retrospectively analyzed data from hybrid closed-loop studies involving young children (1–6 years old, n = 20), children (7–12 years, n = 21), adolescents (13–17 years, n = 15), and adults (>18 years, n = 58) with type 1 diabetes. The coefficient of variation quantified variability of insulin needs during 3 weeks of unrestricted-living hybrid closed-loop use. RESULTS Data from 2,365 nights and 2,367 days in 114 participants were analyzed. The coefficient of variation of insulin delivery was higher in young children compared with adults (mean difference at nighttime 10.7 percentage points [95% CI 2.9–18.4], P = 0.003; daytime 6.4 percentage points [95% CI 2.0–10.9], P = 0.002) and compared with adolescents (mean difference at nighttime 10.2 percentage points [95% CI 0.0–20.4], P = 0.049; daytime 7.0 percentage points [95% CI 1.1–12.8], P = 0.014). CONCLUSIONS Diabetes management in young children is complicated by higher variability in insulin requirements, supporting fast-track clinical practice adoption of closed-loop in this vulnerable population.