procedure TMainForm.CreateMDIChild(const Name: string);   
var  
Child: TMDIChild;   
begin  
{ create a new MDI child window }  
Perform(WM_SETREDRAW, 0, 0); //锁屏幕   
Child := TMDIChild.Create(Application);   
Child.WindowState := wsMaximized; //假设在这里将新建的子窗体设为最大化   
//或设置子窗体的Width和Height都可以   
Child.Caption := Name;   
if FileExists(Name) then Child.Memo1.Lines.LoadFromFile(Name);   
Perform(WM_SETREDRAW, 1, 0); //解锁屏幕并重画   
RedrawWindow(Handle, Nil, 0, RDW_FRAME + RDW_INVALIDATE +   
RDW_ALLCHILDREN + RDW_NOINTERNALPAINT);   
end;