Website with required login

Hopefully someone can help me out. I am building a family-blog. Now we would like to keep the blog private, in such way that only people that have an account can access the blog.

Is there a plugin or something for WP that on first visit of the page shows only a login screen. Only when you are logged in it is possible to see the real blog.

A plugin would be nice, but any other kind of tool to create this kind of functionallity is fine too.

Does anyone know something that can help me out?