Make a Form a Parent (MDIParent) for a child form in C#

Type this inside the event which you call the child MDI form
from the parentMDI form.

Inside Parent Form:

            frmSearchCust frmCSearchCust = new frmSearchCust();
            frmCSearchCust.MdiParent = this;
            frmCSearchCust.StartPosition = FormStartPosition.CenterScreen;
            frmCSearchCust.Show();