ウィンドウを作成して、別の子コントロールを追加できます
<Window x:Class="RetailPOS.Dashboard"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:Child="clr-namespace:RetailPOS.View.Usercontrols.MainWindow"
x:Name="DashBoardCntrl"
xmlns:WpfKb="clr-namespace:WpfKb.Controls;assembly=WpfKb"
Title="MainWindow" Height="768" Width="1024" ResizeMode="NoResize" WindowStartupLocation="CenterScreen" >
<Grid>
<Grid.RowDefinitions>
<RowDefinition></RowDefinition>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition></ColumnDefinition>
<ColumnDefinition></ColumnDefinition>
</Grid.ColumnDefinitions>
<StackPanel Orientation="Vertical" Grid.Column="0">
<Child:MergeUserInfoSearch x:Name="UserInfo" HorizontalAlignment="Left" Margin="1,0,0,0" Width="513"></Child:MergeUserInfoSearch>
<Child:MenuControl x:Name="MenuCtrl" HorizontalAlignment="Left" Margin="1,0,0,0" Width="510"></Child:MenuControl>
<GroupBox Height="159" Margin="8 0 0 0" HorizontalAlignment="Left" VerticalAlignment="Top" Background="AliceBlue" Header="Categories" Width="499">
<Child:Categories x:Name="cat" HorizontalAlignment="Left" Margin="1,0,0,0" ></Child:Categories>
</GroupBox>
<GroupBox Height="360" Margin="5 0 0 0" HorizontalAlignment="Left" Grid.Row="1" VerticalAlignment="Top" Background="AliceBlue" Header="Products">
<Child:Products HorizontalAlignment="Left" x:Name="prod" Margin="1,0,0,0"></Child:Products>
</GroupBox>
</StackPanel></Grid>