I asked DH about this. He gives the pamol (when it's been allowed) and watches closely for the next 30mins. His theory is if he left Child A, a teething unhappy kid, just because he was teething and unhappy, but then found out at a later date another child in the centre, child B, had a nasty illness, then child A may not just be 'teething' on this occasion and you would want them home.
I should ask him if they have a set sending home temp.
They do the carseat thing though to make it easier on everyone. Lol apparently the spares are mainly used by Mums, when Dad's forget to take them out of the car themselves in the mornings