For a basic cold no, I won't close, for something more yes! We recently had strep throat here (me and my son), I closed for a couple of days. We also had fevers too, so that was the main reason for closing. I would also close for a stomach bug and have in the past. I have a hard time saying no too...I also feel guilty when I call them to say I am closed!
I find it odd that no one got your messages tho when you did try to call, that would bother me. Maybe ensure you have an alternate way to contact each parent?
If you still feel terrible later today, tell everyone at pick-up you are closed tomorrow...that way they have no excuse and you get your day to rest.