It's fast forward for a San Francisco start-up publishing an audio magazine, delivered on cassette, for kids. Listen and Learn Home Education has launched Boomerang, a 70-minute monthly mix of current events, music, and humor produced for and by 7- to 12-year-olds. Sold through direct mail to the home market, the magazine boasts more than 3,500 subscribers paying $39.95 a year, according to president David Strohm, who hopes to create channels for add-on educational products. Not supported by advertising, the venture relies on circulation to drive revenues. Retail and newsstand distribution could follow if the bootstrapping company can find capital for expansion. -- Anne Murphy