I am using a MDI parent form that has a childs and they show up very well when they are called up by this parent and i use to intensiate child form as
ChildForm
To create a child from another child, just write it like this:
ChildForm sibling = new ChildForm(); sibling.MdiParent = this.MdiParent; sibling.Show();
Or fire a custom event that the parent can respond to.