Вячеслав Золотов

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:wpfApplication1="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="525">
    <Grid wpfApplication1:NewPropertyHelper.Prop="{Binding}">
        
    </Grid>
</Window>

namespace WpfApplication1
{
    public static class NewPropertyHelper
    {
        public static readonly DependencyProperty PropProperty = DependencyProperty.RegisterAttached("Prop", typeof (object), typeof (NewPropertyHelper), new PropertyMetadata(default(object)));

        public static object GetProp(UIElement element)
        {
            return (object) element.GetValue(PropProperty);
        }

        public static void SetProp(UIElement element, object value)
        {
            element.SetValue(PropProperty, value);
        }
    }
}

public static IEnumerable<T> GetAllChildren<T>(this UIElement frameworkElement) where T : UIElement
        {
            if (frameworkElement == null)
            {
                yield break;
            }
            
            for (var i = 0; i < VisualTreeHelper.GetChildrenCount(frameworkElement); i++)
            {
                var _Child = VisualTreeHelper.GetChild(frameworkElement, i);
                if (_Child is T)
                {
                    yield return (_Child as T);
                }
                var control = _Child as UIElement;
                foreach (var child in GetAllChildren<T>(control))
                {
                    yield return child;
                }
            }
        }