content page load executes first before master page executes and how to get session value from master page to child page

Hi
I am having dropdownlist 'ddlNUmber' in master page
I have a textbox 'txtNumber' in content page(aspx)
if i select value from 'ddlNUmber' that value should come in the textbox of content page
if already (content) page is opened and if i selct dropdownlist value from 'ddlNUmber' that value should come in textbox 'txtNumber' of the content page. This textbox is already available in all the content pages
For getting the solution I have tried this
I have event in master page
public event CommandEventHandler ddlChanged;
In master page dropdownlist 'ddlNumber" selectedindexchanged I am calling
protected void ddlNUmber_SelectedIndexChanged(object sender, EventArgs e) {
ddlChanged(this, new CommandEventArgs(ddlNUmber.SelectedItem.Text, Session["ddlValue"])); }
In the child page I have protected void Page_Init(object sen ...