At run time, MDI child forms are displayed inside the client area of an MDI parent form. An MDI child form can be maximized, minimized, and moved within the MDI parent form. To create an MDI child form, assign the System.Windows.Forms.Form that will be the MDI parent form to the Form.MdiParent property of the child form. You can use the Form.IsMdiContainer property to determine whether a form is an MDI parent form.

You can use the Form.IsMdiChild property to determine whether a form returned by a method or property is an MDI child form or a standard form in your application such as a dialog box.