Is there any way to get all the controls on a container control?

You're looking for the TWinControl.Controls array and the accompanying ControlCount property. Those are for a control's immediate children. To get grandchildren etc., use standard recursive techniques.

You don't really want the Components array (which is what the for-in loop iterates over) since it has nothing to do, in general, with the parent-child relationship. Components can own things that have no child relationship, and controls can have children that they don't own.

Also note that disabling a control implicitly disables all its children, too. You cannot interact with the children of a disabled control; the OS doesn't send input messages to them. To make them look disabled, though, you'll need to disable them separately. That is, to make a button have grayed text, it's not enough to disable its parent, even though the button won't respond to mouse clicks. You need to disable the button itself to make it paint itself "disabledly."

If you disable a panel, al controls on it are disabled too.

Recursive solution with anonymous methods:

type
  TControlProc = reference to procedure (const AControl: TControl);

procedure TForm6.ModifyControl(const AControl: TControl; 
  const ARef: TControlProc);
var
  i : Integer;
begin
  if AControl=nil then
    Exit;
  if AControl is TWinControl then begin
    for i := 0 to TWinControl(AControl).ControlCount-1 do
      ModifyControl(TWinControl(AControl).Controls[i], ARef);
  end;
   ARef(AControl);
end;

procedure TForm6.Button1Click(Sender: TObject);
begin
  ModifyControl(Panel1,
    procedure (const AControl: TControl)
    begin
      AControl.Enabled := not Panel1.Enabled;
    end
  );
end;