Dental decay is a prevalent bacterial disease affecting a significant percentage of children globally. In paediatric dentistry, various materials are available for restoring deciduous teeth, addressing both functional and aesthetic concerns. However, paediatric dentists encounter challenges related to patient compliance, limited working time, and material handling. This study aims to observe the survival rate of bulk-fill composite restorations in paediatric patients over a five-year follow-up. A total of 198 patients aged 0 to 12 years underwent 673 class II restorations on deciduous first molars (1M) and second molars (2M). All restorations were conducted performed by 1 Pediatric DDS resident students from the Paediatric Dentistry Department (Padova University), utilizing using different isolation techniques. Bulk-fill composite restorations were evaluated over a five-year follow-up, and data were collected by a single investigator. After five years, 177 patients and 611 restorations were assessed. The retention rate was higher in primary second molars than in first molars, with fewer marginal dyschromies and less formation of secondary caries. The overall failure rate was higher in primary first molars and primary lower second molars. Bulk-fill composites demonstrated significantly positive performance in terms of retention, maintenance, and marginal dyschromies. Bulk-fill composites are promising materials of choice in paediatric dentistry due to their easy handling and favorable properties. Further research is necessary to compare high and low viscosity bulk-fill composites and assess the impact of different variables on restoration success.