This whole question/subject sums up the differences between large and small businesses, IMO
A large business will usually have enough staff to absorb an absent employee, work-wise.
A small business, like mine, can't.
If one of our staff memebers 'phones in sick tomorrow, for a child or for themselves, I have to go into work with my baby to cover them.
If someone is ill, no problem. If someone 'pulls a sicky' and believe me, it is often obvious, it hurts.
An ill child is non-negotiable, of course and I'm not suggesting that someone leaves an ill child at home, but when in a small team someone is not there it shows.
And yes, we can call in agency staff, but if we call at the last minute they often can't get there very quickly.