New Post: Using ChildWindow and WindowContainer.

You can find samples(XAML/C#/to Test) of all controls in the "liveExplorer app" available here : https://wpftoolkit.codeplex.com/

To reference the Xceed controls, in Visual Studio, add a reference in your project to Xceed.Wpf.Toolkit.dll.
In your xaml file, add :
xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"

To use a childWindow in a WindowContainer, do the following :

<xctk:WindowContainer x:Name="_windowContainer" >
                  <xctk:ChildWindow x:Name="_childWindow" 
                                  Caption="Modaless ChildWindow"
                                  Left="75"
                                  Top="50"
                                  Width="275"
                                  Height="125"
                                  WindowState="Open">
                        <TextBlock Text="This is a regular Child Window" Padding="10"/>
                </xctk:ChildWindow>
                    
                  <xctk:ChildWindow x:Name="_modalChildWindow" 
                                  Caption="Modal ChildWindow"
                                  IsModal="True"
                                  Left="175"
                                  Top="125"
                                  Width="275"
                                  Height="125"
                                  WindowState="Open">
                        <TextBlock Text="This is a modal Child Window" Padding="10"/>
                </xctk:ChildWindow>
</xctk:WindowContainer>