The Young Avengers and the Runaways are two of Marvel's more prominent teenaged superhero teams, and the many similarities between them prompted calls for a crossover. In the midst of Marvel's "Civil War" event, those calls were answered; the purpose of this miniseries is twofold: first, two plug "Runaways", a perpetually low-selling title; and second, to bridge the gap between the first and second volumes of "Young Avengers" (in this later task it was a failure, through no fault of the creative team, because of the protracted delays that have bedevilled the Young Avengers since the summer of 2006; as I write this, we are only now getting new material, and even that is another miniseries designed to further bridge the gap). The creative team is Zeb Wells and Stefano Caselli, who are generally speaking adequate; Wells has the feel of both teams down quite well, and Caselli's art, while it takes some getting used to (and isn't especially youthful), is enjoyable.
Storywise, the Civil War is basically a shoestring to have the teams meet and interact, before they rescue their kidnapped members from the dastardly clutches of SHIELD. Wells is one of many writers who doesn't give the pro-Reg side a fair shake, although he does come up with some quite hilarious bits, such as SHIELD's "adjusted public sympathy rating" which governs the level of force they employ against unregistered heroes (robots are okay to trash, but not kids). The two series have a huge cast, well over a dozen characters, so Wells focusses in on a few of the characters who have logical connections; the two Skrull characters, Teddy and Xavin; the two robots, Vision and Victor; and Chase, Molly, and Speed, in a plot that follows up on the death of a Runaway in the preceding story in that title. There are bits and pieces for most others, with only Patriot and Hawkeye II (especially the latter) really not having much at all. A particular favourite subplot/running joke was Stature's interest/concern for Victor, and the Vision's annoyance at this; Wells presumably has read the various fan observances of Cassie's taste in men. There is also the introduction into the Marvel Universe proper of Marvel Boy, from Grant Morrison's miniseries of the same name, and Wells handles him quite well too.
If there is a real complaint about this, it is that, while enjoyable, the Young Avengers ultimately turned out to have far more important status quo changes forced upon them by the Civil War, changes that were not really addressed in any concerted fashion for a year and a half or more, and, looking back, it might have been preferable to get something that examined their status with their parents, and (especially) their reaction to Cassie's defection later on. All the same, this is a very enjoyable, isolated adventure for both teams, well worth getting for fans of either or both.