I always find a way to tell parents about changes either in conversation or during my newsletter. It doesn't mean that I say the whole scoop on why but at least they know and I can address it and make sure they don't think someone left because of something I did and that I am trying to cover it up
We have a close-knit group where all the parents know the kids' names and greet them at pickup/drop off. It would be obvious if someone just disappeared or was no longer in the newsletter with their pictures every month.
If you have a pretty close group then the parents would have asked you at some point anyways "Where is Billy and Sammy?" Addressing it up front shows you have nothing to hide.
I also let parents know a few weeks in advance if someone new is coming. Usually I announce it in my newsletter and write whether it's a boy or girl and their name and age.
Personally...I think you did nothing wrong.I think having open, honest communication lines between daycare and the parents fosters trust and honesty. Communication is really important and it probably gives the parents peace of mind.