How to set a mdi child on top of other mdi child

 I have situation

I opened two mdi child forms form one 1st and then form 2 so form 1 on bottom and form 2 on top of 1st but when  I am clicking hide button of mdi parent that is on splitter and when we click it it hide the left side menu.

But when we clicking on hide form-1 comes on top of form-2.Image may be NSFW.
Clik here to view.

Code on hide button click event

private void button1_Click(object sender, EventArgs e)        {            splitPos = splitter2.SplitPosition;            btnView.Visible = true;            btnHide.Visible = false;            splitter2.SplitPosition = 0;            this.BackgroundImage = Resources.SiteScreen;                    }