procedure TForm1.FormCreate(Sender: TObject);
var
  i: integer;
begin
  for i := 0 to Pred(TWinControl(Sender).ControlCount) do
    TWinControl(Sender).Controls[i].?????:= @FormMouseMove;
end; 

procedure TForm1.FormCreate(Sender: TObject);
var
  i,j: integer;
begin
  for i := 0 to Pred(TWinControl(Sender).ControlCount) do
    begin
      if (TWinControl(Sender).Controls[i] is TPageControl)
        then
          begin
            TChildControl(TWinControl(Sender).Controls[i]).OnMouseMove:= @FormMouseMove;

            for j:= 0 to Pred(TWinControl(TPageControl).ControlCount) do
              begin
                TChildControl(TWinControl(TPageControl).Controls[i]).OnMouseMove:= @FormMouseMove;
              end;
          end
        else
          TChildControl(TWinControl(Sender).Controls[i]).OnMouseMove:= @FormMouseMove;
    end;
end; 

[Window Title]
Error

[Content]
Project project1 raised exception class 'External: SIGSEGV'.

 At address 4354A0

[OK]

procedure TForm1.FormCreate(Sender: TObject);
var
  i,j,k: integer;
  PC: TPageControl;
  TS: TTabSheet;
begin
  PC:= nil;
  TS:= nil;

  for i := 0 to Pred(TWinControl(Sender).ControlCount) do
    begin
      if (TWinControl(Sender).Controls[i] is TPageControl)
        then
          begin
            PC:= TPageControl(TWinControl(Sender).Controls[i]);
            TChildControl(PC).OnMouseMove:= @FormMouseMove;

            if PC.PageCount > 0
              then
                for j:= 0 to Pred(PC.PageCount) do
                  begin
                    TS:= TTabSheet(PC.Controls[j]);
                    TChildControl(TS).OnMouseMove:= @FormMouseMove;

                    for k:= 0 to Pred(TS.ControlCount) do
                      TChildControl(TS.Controls[k]).OnMouseMove:= @FormMouseMove;
                  end
              else
                Continue;
          end
        else
          TChildControl(TWinControl(Sender).Controls[i]).OnMouseMove:= @FormMouseMove;
    end;
end;   

procedure TForm1.ApplicationProperties1UserInput(Sender: TObject; Msg: Cardinal
  );
var
  WC: TWinControl;
  Ctrl: TControl;
begin
  //MC:= FindControlAtPosition(Mouse.CursorPos,True);
  WC:= FindLCLWindow(Mouse.CursorPos);

  if Assigned(WC) then
    begin
      case Msg of
        LM_MOUSEMOVE:
              begin
                Label2.Caption:= WC.Name;
              end;

        LM_LBUTTONDOWN:
              begin
                Label1.Caption:= WC.Name;

                case PageControl1.ActivePageIndex of
                  0: ClosePanel(WC,WC.Parent, mbLeft);//TabSheet1
                  1:
                    begin
                      Ctrl:= TabSheet2.ControlAtPos(TabSheet2.ScreenToClient(Mouse.CursorPos), True,True);
                      if Assigned(Ctrl) and (Ctrl is TWinControl)
                        then ClosePanel(TWinControl(Ctrl), TWinControl(Ctrl).Parent,mbLeft);
                    end;
                end;


              end;

        LM_RBUTTONDOWN:
              begin
                //if PageControl1.ActivePage = TabSheet1 then ClosePanel(WC, WC.Parent,mbRight);
                ClosePanel(WC,PageControl1.ActivePage,mbRight);
              end;
      end;
    end;
end;
...
procedure TForm1.ClosePanel(Sender, AParent: TWinControl; MB: TMouseButton);
begin
  case MB of
    mbLeft:
          begin
            if (TWinControl(Sender).Parent = AParent) and not (TWinControl(Sender) = FPnl) then
              if Assigned(FPnl) then FreeAndNil(FPnl);
          end;
    mbRight:
          begin
            if (TWinControl(Sender) = AParent) or (TWinControl(Sender).Parent = AParent) then
              if Assigned(FPnl) then FreeAndNil(FPnl);
          end;
  end;
end;