<b><i>Introduction:</i></b> Dupilumab has recently been shown to be effective in children under 6 years of age with atopic dermatitis (AD). Nevertheless, real-life and long-term follow-up data are scarce. We aimed to assess the effectiveness, safety, and long-term outcomes of dupilumab in a daily-practice setting in this age group. <b><i>Method:</i></b> This was a retrospective observational cohort study. Only patients with 16 or more weeks of treatment were included in the analysis. The proportion of patients who achieved ≥75% or 90% reduction from baseline EASI (EASI75 and EASI90, respectively) and the percentage of patients who achieved vIGA 0–1 were analyzed at 4, 16, 48, 72, and 96 weeks (when available). Adverse events were recorded during follow-up. <b><i>Results:</i></b> A total of 19 patients <6 years old with moderate-to-severe AD were included in the cohort, with a median age of 4.7 years (range: 2.6–5.9). The median weeks on dupilumab were 51.3 (IQR: 24.6–79.3). EASI75 was achieved in 11/19 patients (57.9%) at w4, 16/19 (84.2%) at w16, 9/12 (75%) at w48, 6/6 (100%) at w72, and in 2/2 (100%) at week 96. The objective of vIGA 0–1 was reached by 10/19 patients (51.6%) at w4, by 14/19 (73.7%) at w16, by 9/12 (75%) at w48, by 5/6 (83.3%) at w72, and by 2/2 (100%) at w96. Dupilumab was discontinued in 3 patients (15.8%) due to loss of response. One patient developed a paradoxical palmo-plantar eruption. We found no cases of conjunctivitis, facial erythema, or injection-site reactions related to dupilumab. <b><i>Conclusions:</i></b> Dupilumab was effective and safe in our cohort of patients with moderate-to-severe AD under 6 years of age. Response was maintained in the long term in most patients with longer follow-up. Its adverse effect profile was similar to that found in older children and adults.