Show opened form ismdicontainer C#

Question

I use form with option

IsMdiContsiner = True

Need when click on button to show child form in container

If is opened to show that opened child form, if not opened to open new

 

private void KnjigaIzlaznihFakturaToolStripMenuItem1_Click(object sender, EventArgs e)
       {
           _6102_KIF newMDIChild = new _6102_KIF
           {
               MdiParent = this
           };
           newMDIChild.Show();
       }