I'm probably being unreasonable as DD catches all the colds and bugs anyway so this is not a big deal in the scheme of things, but as we left nursery I saw DD's sun-hat get plonked on another child's head.
There is a known case of headlice in the nursery though (albeit in a different room) so should I say something about not sharing hats or is it not worth bothering about because they'll all catch everything at some point!! 