The Sarah Jane Adventures, CBBC (UK)
BBC; IMDb; TV.com; TV Tropes; Wikipedia
This is sort of a spin-off of the more recent series of Doctor Who. The title character, Sarah Jane Smith, was one of the many travelling companions the Doctor had over the years, back on the original series. But this series was prompted, I guess, from her having guest-starred in an episode of the new series. (Back in 1981, it should be noted, the character also starred in a spin-off called K-9 and Company, which never made it past the pilot.) In any event, Sarah Jane is aware that there are aliens appearing on Earth fairly often, for reasons ranging from visiting, to crash landing, to invasion. Sometimes she'll help them out, and sometimes she has to put a stop to their plans. I guess. It should also be noted that this is set in an era where, on the new Doctor Who series, aliens have become known by the general public to exist, though this knowledge hasn't really changed how people go about their lives. It's not like there's official contact or anything, and even now many people still don't believe in aliens. It should further be noted that there exist agencies like UNIT and Torchwood to deal with aliens and such things, though Sarah Jane prefers to handle things differently than they would.
Well, anyway. For a long time now, she's been alone. She doesn't want to put anyone in danger, and besides, most people wouldn't believe anything she has to say, anyway. But in the pilot episode (or technically a "holiday special" that aired before the series and set up the plot), she's investigating a soda company that is run by aliens called the Bane, who have an evil plot to take over the world and make it their new home. Meanwhile, a teenage girl named Maria Jackson, has just moved in next door to Sarah Jane, along with her father, Alan (presumably no relation to country singer Alan Jackson). Alan is amicably divorced from Maria's mother, Chrissie, who pops in now and then. Anyway, Maria gets mixed up in the whole situation with the Bane, and learns the truth about Sarah Jane and all she does. In the course of the adventure, the two of them meet an apparently teenage boy, who the Bane had created as part of their plot, and since he's actually brand new, never having been born or raised or anything, he doesn't know anything about the world. Though he does have the brain power of like 10,000 people who the Bane had scanned to create him. Anyway, he wants to get away from them, and Sarah Jane "adopts" him, giving him the name Luke Smith. He'll help Sarah Jane and Maria on their adventures, I guess.
I should also mention that Sarah Jane has a number of alien artifacts that may come in handy, as well as an advanced computer system called "Mr. Smith" (perhaps it's even an AI, I dunno), which is useful for all sorts of things, hacking other computers and whatnot. And in the first regular episode of the series, the team gains another member, Clyde Langer, who goes to school with Maria and Luke. And that's about all I can say so far. Um, I think I saw the whole first season on Sci-Fi Channel, but I don't think any other seasons have aired yet in the U.S., so I'm not sure if or when I'll see the rest of the series.