Having one navigation button password protected covering all children

I want to be able to click one navigation button on my website that is protected with a password and once the password is typed in it would give access to all the child pages under the button. Right now I have the Member Login button password protected, but, I can still open all the child pages without the password. If I password protect each and every child page it becomes a bit tedious for visitors to keep plugging in passwords for each child page and if I keep them public then they are not protected. Can anyone help with this? http://www.fmcleamington.org