Lung ultrasound, a non-invasive bedside technique for assessing paediatric patients with acute respiratory diseases, is becoming increasingly widespread. The aim of this prospective, observational cohort study was to evaluate the effectiveness of a clinical ultrasound score in assessing infants with acute bronchiolitis in the emergency department and its ability to accurately identify patients at a higher risk of clinical deterioration. Infants under 6 months of age with clinical symptoms compatible with acute bronchiolitis were enrolled and underwent clinical and lung ultrasound evaluations. The study included 50 patients, the median age of which was 2.2 months (IQR: 1–5), and the primary outcome was respiratory support. Infants requiring invasive or non-invasive ventilation showed higher scores (5 points [IQR: 3.5–5.5] vs. 2.5 [IQR: 1.5–4]). The outcome had an AUC of 0.85 (95%CI: 0.7–0.98), with a sensitivity of 87%, specificity of 64%, and negative predictive value of 96.4% for a score <3.5 points. Children who scored ≥3.5 points were more likely to require respiratory support within the next 24 h (estimated event-free survival of 82.9% compared to 100%, log-rank test p-value = 0.02). The results suggest that integrating lung ultrasound findings into clinical scores when evaluating infants with acute bronchiolitis could be a promising tool for improving prognosis.