The Teen Titans are a group of young heroes in the DC Universe. They started out as a team of sidekicks to more established heroes, such as Aqualad, Robin, Speedy, and Wonder Girl. This membership expanded overtime to include many teenage heroes who need guidance. The Titans has become a place where young heroes can learn to better manage their powers, and hang out with other kids who understand them.
If you are going to buy comic books for your child, remember that most comic books are not for kids anymore. They are written for adults. Most comic books published by DC have a handy rating system on the cover to determine whether or not they are appropriate. If you're not sure, you should probably read the comic book for yourself before giving it to your child. Who knows? You might discover that you enjoy it too!