C-Sharp WPF Grid Visibility

MyGrid1.Visibility = Visibility.Hidden
MyGrid2.Visibility = Visibility.Visible

//extension
public static List<T> GetChildsLike<T>(this object parent) where T : DependencyObject
{
    List<T> logicalCollection = new List<T>();
    GetChildsLike(parent as DependencyObject, logicalCollection);
    return logicalCollection;
}

private static void GetChildsLike<T>(DependencyObject parent, List<T> logicalCollection) where T : DependencyObject
{
    IEnumerable children = LogicalTreeHelper.GetChildren(parent);
    foreach (object child in children)
    {
        if (child is DependencyObject)
       {
            DependencyObject depChild = child as DependencyObject;
            if (child is T)
                logicalCollection.Add(child as T);

            GetChildsLike(depChild, logicalCollection);
       }
   }
}

private void button_NEXT_Click(object sender, RoutedEventArgs e)
{
List<Grid> MyGrids             = new MainWindow().GetChildsLike<Grid>()
                        .Where(x => x.Name.ToLower().Contains("my"))  
                        .OrderBy(x => x.Name.Substring(x.Name.Length -1, 1)).ToList(); 

MyGrids.Visibility = Visibility.Hidden
MyGrids[1].Visibility = Visibility.Visible
}