A large district general hospital is reviewing its paediatric Emergency Department activity as part of a service redesign project.

During a multidisciplinary governance meeting, anonymised attendance data over the past 12 months is presented. The analysis highlights significant variation in attendance rates across different paediatric age groups.

The clinical lead notes that a particular age group consistently accounts for the highest proportion of Emergency Department visits, often with non-specific presentations such as feeding concerns, irritability, and transient physiological changes, frequently leading to diagnostic uncertainty and lower thresholds for attendance.

Which of the following groups has the highest rate of Emergency Department attendance?