If they're in Pasadena, they can drive west south on the 110 through downtown, and head west on the 10 (Santa Monica Freeway) until it stops at the beach. There is plenty of parking if they go early.
Here's an earlier thread about the paths and a link. It's very easy to follow, although they will have to detour through Marina del Rey.
http://www.bikeforums.net/showthread.php?t=270137
http://www.bikely.com/maps/bike-path...eack-Bike-Path
If they don't mind a few hundred feet of (not terribly steep) climbing, they can go to the lookout on the Palos Verdes Peninsula for some spectacular views. It's only 3 additional miles and the view is worth it.
http://www.bikely.com/maps/bike-path...-to-PV-Viewing
If they want to go farther, they can follow PV South through some easy rollers for several more miles. It's quite picturesque.