Автор: http://www.swissdelphicenter.ch

unit Child;

 // Have you noticed that when you try to close a MDIChild form 
// the form minimizes but doesn't disappear from your Main form 
// client area? 
// 
// With this tip you can learn how to really close the MDI child 
// form and free the memory occupied by the form 


interface

 uses
   Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;

 type
   TMDIChildForm = class(TForm)
     procedure FormClose(Sender: TObject; var Action: TCloseAction);
   private
     { Private declarations }
   public
     { Public declarations }
   end;

 var
   MDIChildForm: TMDIChildForm;

 implementation

 {$R *.DFM}

 procedure TMDIChildForm.FormClose(Sender: TObject;
   var Action: TCloseAction);
 begin
   // This line of code frees memory and closes the form 
  Action := caFree;
 end;

 end.