PrintPreview/ Print datagrid in MDI

Hi Guys,
I have some MDI C# project.
The "main" window opens childs:

Code:

---

            SomeType1 childForm = new SomeType1;
            childForm.MdiParent = this;
            childForm.Show();

        ...

            SomeType2 childForm = new SomeType2;
            childForm.MdiParent = this;
            childForm.Show();

---

...

Each "childForm" has its own DataGrid placed on it.
I need to implement print preview / print functionality.

I've placed some stuff like this:

Code:

---

        private void printPreviewToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form activeChild = this.ActiveMdiChild;
            printPreviewDialog1.ShowDialog(activeChild);
        }

---

But preview dialog is empty...

How to do it?
Thanks in advance.