I got it. Sometimes, it takes asking the question to find the answer. I was trying to use the properties and events from a timer, and forgot to mention the window, as in Window.MyRectangle1.MyProperty. I found back my children (and some of my marbles)
From outside of the window you need to prepend the control name with the window instance variable name:
Window1.MyRectangle1.MyProperty
Prepending the control name with Window doesn’t make much sense to me. Window is a property on the Control class and returns the parent of the control, usually the window.