This will add two buttons to the Canvas at runtime. On the "Get Children" button click, it will loop through the children and display the text of the Button.

XAML:
Code:
<Window x:Class="WpfApplication6.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1" Height="318" Width="489">
    <Grid>
        <Canvas 
            x:Name="canvas1" 
            Height="100" 
            HorizontalAlignment="Left" 
            Margin="116,62,0,0" 
            VerticalAlignment="Top" 
            Width="200">
            
        </Canvas>
        
        <Button 
            x:Name="btnGetChildren" 
            Content="Get Children" 
            Height="23" 
            Margin="174,209,218,47" 
            Width="75" 
            Click="btnGetChildren_Click" />
    </Grid>
</Window>
Code:
Code:
public partial class Window1 : Window
{
    public Window1()
    {
        InitializeComponent();

        this.Loaded += new RoutedEventHandler(Window1_Loaded);
    }

    void Window1_Loaded(object sender, RoutedEventArgs e)
    {
        StackPanel sp = new StackPanel();
        sp.Orientation = Orientation.Vertical;

        Button b = new Button();
        b.Content = "Button 1";

        Button b1 = new Button();
        b1.Content = "Button 2";

        sp.Children.Add(b);
        sp.Children.Add(b1);

        canvas1.Children.Add(sp);
    }

    private void btnGetChildren_Click(object sender, RoutedEventArgs e)
    {
        foreach (UIElement element in canvas1.Children)
        {
            if (element is StackPanel)
            {
                StackPanel sp = element as StackPanel;

                foreach (UIElement spElement in sp.Children)
                {
                    if (spElement is Button)
                    {
                        Button b = spElement as Button;
                        MessageBox.Show(b.Content.ToString());
                    }
                }

            }
        }
    }
}