How to pass child page control values to Parent page controls?

Question

I have main page customer.aspx i enter the data and then iam giving one button on that page when i click that button one papup window open that is insurance.aspx ,
now i fill the form and then save the data after  submit the data to database window will close and that controles data

like insurance name will come and appear in parrent page customer.aspx having one controle ,txtinsurance

plz any one help me