Even if measles hadn't been confirmed, if there was something going around nursery that was severe enough to have put the first two kids that got it into hospital, then I would certainly expect nursery to be sending home letters about the problem, the fact that it has already hospitalised two kids, symptoms to look out for and about going to see the gp as it can be really serious etc.
Even if they don't actually say that it is measles.
I don't think that is panic mongering - I think it is showing consideration for others that you and your family come in to close contact with regularly. It should also help to prevent people going out and about if they suspect there might be a problem, rather than thinking that it was just a bit of a cold and going out and then spreading it further.
I say that as someone who wasn't vaccinated against measles as a child - apparently there was a scare around the time I was due to get it so my mother didn't get me done, although she did get my younger sis done when she was ready as the scare had died down by then. She realised when I started back at junior school that I had missed my vaccination so rang up the gp, who ordered it and I went down for my appointment a few days later. I had a bit of a cold so he said it would keep in the fridge and to come back when I was healthy again.
next day was start of term - I was still a bit sniffly but nothing major so went into school. Couple of days later - cold hadn't gone and I was covered in spots - yep, come down with measles and managed to give it to quite a lot of kids in the school as I'd gone in whilst contagious (although I didn't know obviously at the time). It was a small town, same doctors practice saw everyone, so lots of people in my year hadn't had the vaccination. However, once the doctor saw that I had measles (back in the day when they did house calls!) they were able to tell school who were able to warn everybody and for a while if people had colds then parents were warned to be extra careful and keep them off maybe more than they would have done otherwise, so they didn't come and spread measles around even more. This was seen as better than going in regardless and assuming that it was just a mild cold that you had.
Reading reports about the current outbreak of measles, it seems that one of the things they are saying is that being vaccinated doesn't mean that you won't get measles but that if you do get it, it should be less severe than it would have been otherwise. It sounds like the version going around your nursery is causing severe problems (you wouldn't normally expect 2/2 cases to end up in hospital) so they should be alerting people to potential dangers