I left the industry in the early 90s, but throughout the 80s I worked as a professional actor. Unless things have changed dramatically (pun intended), there is no such thing as "volunteer work" on a professional set. Film and television production is heavily unionized and, without a union card, your son is not going to get a crew position in LA. Even positions like production assistants, essentially gophers, require the right connections. This is not to say that your son should give up his dreams, but the likelihood of his getting anywhere near a professional set or location shoot during a one-week vacation is nil.

As for "meeting movie stars," you won't see them on the streets of Hollywood, which is a really chintzy, touristy place. Paramount is the largest studio in Hollywood, and there are a number of smaller ones that you almost certainly have never heard of. However, all of them are closed compounds with heavy security -- a tour or tickets to a taping is the only way you'll get on a lot. Universal, Warner Brothers, Disney and NBC are in the Valley. Sony Pictures is in Culver City. Fox is in West Los Angeles. The suggestion about restaurants is okay, I suppose, but I've seen more "names" in restaurants in neighborhoods where they live than in the so-called "power" restaurants, and the latter are prohibitively expensive. Finally note that the industry, like most everything else in the US, shuts down for the holidays.

I don't mean to sound discouraging, but the film and television industry is insular and protected. Every year, thousands and thousands of young people come here, hoping to get into the industry. It's not impossible, but it takes time and considerable effort. It's not something someone does on a one week vacation.