Martin,

To determine if the active MDI child is minimized you can use the MDI parent containers ActiveMdiChild property which you can then proceed to check or set the WindowState property.

MessageBox.Show(this.ActiveMdiChild.WindowState.ToString());

If you wanted to loop through all MDI children regardless of them being active or not, use the MDI parent containers MdiChildren property which will yield an array of MDI forms.

for (int nForm = 0; nForm < this.MdiChildren.Length; nForm++)
{
   MessageBox.Show(this.MdiChildren[nForm].WindowState.ToString());
}

In both of these examples the forms WindowState enumeration is used and can be set to one of the following.

Maximized
Minimized
Normal

Regards
Neil