The Juul e-cigarette was created to help adult smokers quit, according to the company that makes it. Its developers wanted to make the experience of getting a stimulating hit of nicotine dramatically better than sucking on a stinky, smoking stick of burning tobacco. Their success made Juul the top-selling e-cigarette in the U.S. in two years, but it achieved that position in part by attracting a huge following among kids younger than 18, who aren’t legally allowed to purchase such products. [...]