Refer to control on parent form

I have a MDI container form "frmParent". On that form there is a tabstrip control with 2 pages. On one of those pages there is a textbox and a button.

When the user clicks on the button a child form is opened inside the container form "frmChild" which displays a datagrid. The WHERE clause in the select statement which is bound to the grid comes from the textbox on the Parent form.

How do I refer to this textbox control ?

Thanks in Advance

You can make a public property for the text property of the textbox or you can use a delegate.