Recently (Oct. 4), Roblox skipped even deprecating these properties and went straight to removing them. It seems that Roblox did a clear-up of API bloat in this recent update, but ended up removing some genuinely useful features.
Both of these properties had genuine use-cases, and now have to be substituted by either iterating through the contents of either GUI container, or by making a frame that contains all of the contents.
I would like to propose that these properties be re-added, as I have been using them frequently in my code, and I am sure many others have also been doing so.