how to close all open child forms in MDI parent through Program.cs class

Iterate each open child form and put them into a list

for (int i1 = 0; i1 < Application.OpenForms.Count; i1++)
{
        Form f = Application.OpenForms[i1];
         
         if (f.IsMdiChild)          
         lst.Add(f);
       
}

Then close all the forms:

while (lst.Count > 0)  
{       
         Form f = lst[0];
        f.Close();
        f.Dispose();
        lst.RemoveAt(0);

}

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