There's no law about hanging out in public places where teens meet. The trick is breaking into the clique with approval. Someone here had a similar problem and managed to break his way into a creative writing club that the local junior high was having at a local starbucks.

You could talk with school teachers as part of your research as a writer. They would be closer to an age you would feel comfortable with, able to give you insight into real character, and possibly give you ideas on how to meet the parents of other kids the age you're looking for.

I wish you the best of luck.