Как определить дочерние окно

var wnd,cwnd:HWND;
..........................
function EnChWndCallBack(FormHandle:hWnd;l:pchar):boolean;stdcall;
var FormClass:array[0..255] of char;
begin
Result:=True;
GetClassName(FormHandle, FormClass, sizeof(FormClass));
if FormClass=string(l) then
 begin
  cwnd:=FormHandle;
  Result:=false;
 end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
wnd:=FindWindow(pchar('TFChatForm'),nil);
if wnd<>0 then
begin
EnumChildWindows(wnd,@EnChWndCallBack,LParam(pchar('TMemo')));
if cwnd<>0 then
 begin
  SendMessage(cwnd,WM_SETTEXT,0,LParam(pchar('My Message Text!')));
  PostMessage(cwnd,WM_KEYDOWN,VK_RETURN,0);
 end;
end;
end;