I think you’re misunderstanding the term sessions and what they do.
HTTP (or the internet) is stateless, IE: it doesn’t remember anything from page to page.
To combat this we use various methods, cookies, sessions, databases etc.
If I log in to your website, the session that is created is for my browser only - you will get a different session - the same, but different as it only exists in your browser.
When an admin logs in and changes content, i can see that content next time the page is refreshed.
If you want to put a notification (like facebook) then you need to ‘push’ that to the server.
Have a read of this wiki which explains far better than i can what pushing data requires.
Hope that helps,
Red