= 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 $5(0.0442)\simeq0.221$. A crude rare-event approximation gives about a \b[22% chance] of at least one attendance.
A constant-rate <Poisson process> instead gives
$$
\boxed{\mathbb P(\text{at least one attendance})\simeq1-e^{-0.221}\simeq0.20.}
$$
Thus \b[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.
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