 Solution

The control attendance rate is approximately $0.0442$ per child-year. Assuming that rate is roughly constant over the first five years, expected attendance count is $5(0.0442)\simeq 0.221$. A crude rare-event approximation gives about a 22% chance of at least one attendance.

A constant-rate Poisson process instead givesThus roughly one child in five is the appropriate order of magnitude. An attendance rate counts recurrent attendances, whereas a first-attendance risk counts children. The aggregate rate alone does not identify that risk without assumptions about recurrence and age-specific incidence; the Poisson conversion makes those assumptions explicit.