We do it with playgroup, but that's all of us together, because we have a FB group.

I guess I see parties as quite different. Thinking through the parties I've been to for DS1 though (about 20 - not heaps, but a fair few now) it just would never have occurred to me that the birthday child's parents would do a ring around to say someone with a cold might be attending.

The earlier step hadn't ever occurred either (but clearly happened, given the OP's post!) of someone calling to say that their child had a cold, and were they allowed to still come ...

I guess I see things as a bit more clear cut - if my child is sick and possibly contagious (like they both are at the moment!) then I wouldn't be taking them to a party (and indeed, there's a birthday party I'd very much like to go to on Saturday - but there's kids, there's a pregnant lady, my kids are a bit sick, I'm on the mend from something myself, and so sadly, we won't be attending). If my child has a bit of a snotty nose but they're teething, or they're just affected by the season, and I am sure that they aren't sick, then I'd go.

If I barred them from every activity when they had a runny nose, we'd be housebound all winter.

But if they're sick, they might pass it along to other kids, they might spoil the party for the other children, they might get sicker, and their discomfort might be prolonged. None of which I want! So we'd stay away.

If it was me who was particularly concerned though, and I and my kids were healthy, and I thought that people with colds might have notified the host, I'd call to find out. Sure it might seem a bit silly, but the thought of that doesn't bother me much.

Maybe this is an etiquette that will become more apparent at kinder? I just haven't come across it yet. Not aiming to diss it - I just don't get it.