how to pass data between MDI child forms/not MDI to child but child to child!

Here is a thing. I have three forms, a MDI container, child1 and child2. Now i want to pass some text box value from child1 to child to while both are in the MDI container form.
problem....
        1. I can pass the data but when child2 pops up it will be out of MDI container.
        2. when i create a new instance of child2 by making it MdiParent i get error saying child one is not a mdicontainer.
I'm sure u gon figurout what i mean. Here is the code.
                  on child1 form
child1 w = new child1();
w.MdiParent = this;
w.CodeText = txtcode.Text;
w.Show();
               on child2 form
public String CodeText
{
get { return label1.Text; }
set { label1.Text = value; }
}
string name = lable1.text;
pls help!!!