Two animated series debut this week

A couple of animated series begin this week: one for grown-ups, and one for children.

"Robot Chicken," premiering 10:30 p.m. Sunday, is a hilarious addition to Cartoon Network's Adult Swim block.

Aptly described by co-creator Seth Green as "like 'Saturday Night Live' with stop motion -- only funnier," this new show presses toys into service as the stars of scathingly funny sketches spoofing everything from C-SPAN and "Pokemon."

"Robot Chicken" is the coolest way for grown-ups to have fun with action figures.

And for the children, there's "Avatar: The Last Airbender" premieres on Nickelodeon with a special one-hour edition 6 p.m. Monday, then airs Fridays from 7 to 7:30 p.m.

A cartoon series in the anime style, "Avatar" centers on Aang, a fun-loving 12-year-old who must forgo a normal life to master his latent powers over the four elements, especially the hostile Fire Nation, which threatens to enslave the Water, Earth and Air Nations.

Other shows to look out for:

* Legal analyst Nancy Grace is part of a personality injection for CNN Headline News, which starting Monday will interrupt its nonstop news flow for a three-hour block of signature weeknight programming. At 7 p.m., "Nancy Grace" stars the ex-prosecutor on a talk show that will analyze the day's important cases, with guests ranging from legal experts to inmates and victims of crime.

* Bonnie Franklin and former TV daughters Valerie Bertinelli and Mackenzie Phillips reunite for a "One Day at a Time" special. The Norman Lear-created sitcom, which ran from 1975 to 1984, was pioneering as it focused on a single-parent family. CBS trots out the reunion Tuesday at 8 p.m.

* "Peter Jennings Reporting: UFOs -- Seeing is Believing" aims to take a fresh look at the phenomena. This two-hour ABC News special tracks the full scope of the UFO experience, from the first famous sighting by Kenneth Arnold in 1947. Although an admitted skeptic, Jennings concludes: "There are important questions that have not been completely answered -- and a great deal not fully explained." The program airs 7 p.m. Thursday.