Finding UserControl in Window WPF

I have a window that has a wrap panel.  In that wrap panel I have placed some viewboxes.  In each of the viewboxes I have placed a simple usercontrol.  How do I assign properties to my usercontrols?  I just can't figure out how to drill down and get to my usercontrol properties.  Sorry I have no code to give as a starting point as I am clueless.  Here is my xaml for the page, if that helps:

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:WPF_Custom_Control="clr-namespace:WPF_Custom_Control;assembly=WPF_Custom_Control" x:Class="Window1"
    Title="Window1" Height="1080" Width="1920">
    <Grid>
        <WrapPanel HorizontalAlignment="Left" Height="934" Margin="10,10,0,0" VerticalAlignment="Top" Width="1892">
            <Viewbox Height="100" Width="100" Stretch="Uniform" StretchDirection="Both" Name="vb1">
                <WPF_Custom_Control:UserControl1/>
            </Viewbox>
            <Viewbox Height="100" Width="100" Stretch="Uniform" StretchDirection="Both" Name="vb2">
                <WPF_Custom_Control:UserControl1/>
            </Viewbox>
            <Viewbox Height="100" Width="100" Stretch="Uniform" StretchDirection="Both" Name="vb3">
                <WPF_Custom_Control:UserControl1/>
            </Viewbox>
            <Viewbox Height="100" Width="100" Stretch="Uniform" StretchDirection="Both" Name="vb4">
                <WPF_Custom_Control:UserControl1/>
            </Viewbox>
            <Viewbox Height="100" Width="100" Stretch="Uniform" StretchDirection="Both" Name="vb5">
                <WPF_Custom_Control:UserControl1/>
            </Viewbox>
            <Viewbox Height="100" Width="100" Stretch="Uniform" StretchDirection="Both" Name="vb6">
                <WPF_Custom_Control:UserControl1/>
            </Viewbox>
            <Viewbox Height="100" Width="100" Stretch="Uniform" StretchDirection="Both" Name="vb7">
                <WPF_Custom_Control:UserControl1/>
            </Viewbox>
            <Viewbox Height="100" Width="100" Stretch="Uniform" StretchDirection="Both" Name="vb8">
                <WPF_Custom_Control:UserControl1/>
            </Viewbox>
            <Viewbox Height="100" Width="100" Stretch="Uniform" StretchDirection="Both" Name="vb9">
                <WPF_Custom_Control:UserControl1/>
            </Viewbox>
            <Viewbox Height="100" Width="100" Stretch="Uniform" StretchDirection="Both" Name="vb10">
                <WPF_Custom_Control:UserControl1/>
            </Viewbox>
        </WrapPanel>
        <Button Content="Button" HorizontalAlignment="Left" Margin="116,1003,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click"/>

    </Grid>
</Window>

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Thank you for any help on this.