[ecfisa]

Hola mjjj.

Probá de este modo:

Código Delphi [-]
type
  TfrmMain = class(TForm)
   ...
  private
    function GetForm(AName: string): TForm;
  ...
  end;
...

implementation
...

function TfrmMain.GetForm(AName: string): TForm;
var
  i: Integer;
begin
  Result:= nil ;
  for i:= MDIChildCount-1 downto 0 do
    if MDIChildren[i].Name = AName then
      Result:= MDIChildren[i];
end;
...

LLamada de ejemplo:

Código Delphi [-]
procedure TfrmMain.Button1Click(Sender: TObject);
begin
  GetForm('Form2').Caption:= 'Nuevo Caption';
  GetForm('Form2').Color:= clLime;
  ...
end;

Saludos.