Modify this C# WPF application to do something extra

Hi there I need you to modify this application so that a child content control is added to the Designer Canvas once one of the items are double clicked. Here is the application: [login to view URL] I want to build a the object-hierarchy as attached picture. Each time a child element is added, all the element should reposition in order to give the hierarchy perception. I don't mind the project losing functionality of moving and resizing, so you can change that as you please.