I have .net 1.1 WinForms MDI application.

I need to close all MDI child forms.
I tried

private void CloseAllForms_Click(object sender, System.EventArgs e){

foreach (Control c in this.Controls) {
  if (c is MdiClient)
    ((Form)c).Close();
  }
}

but got error

"Unable to cast object of type 'System.Windows.Forms.MdiClient' to type 'System.Windows.Forms.Form'."

Why ?

I also tried c.FindForm().Close();
but this closes whole application.