Finding ALL child controls WPF

You can use these.

 public static List<T> GetLogicalChildCollection<T>(this DependencyObject parent) where T : DependencyObject
        {
            List<T> logicalCollection = new List<T>();
            GetLogicalChildCollection(parent, logicalCollection);
            return logicalCollection;
        }

 private static void GetLogicalChildCollection<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);
                    }
                    GetLogicalChildCollection(depChild, logicalCollection);
                }
            }
        }

You can get child button controls in RootGrid f.e like that:

 List<Button> button = RootGrid.GetLogicalChildCollection<Button>();