You can hide the Bookmarks Toolbar via "Cmd+Shift+B" if that is what your are taking about. *https://support.mozilla.org/en-US/kb/bookmarks-toolbar-display-favorite-websites If they know where to look, then they can always find your bookmarks. You should create a separate OS user account for your children and protect your account with a password if you do want your children to see your bookmarks and history.