A paintball playing field, a lawn-care business, a pet-grooming service, pre-mixed jars of ingredients for making pastries, a smoothie store in a school cafeteria, and an online jewelry collection: All of these businesses were founded by teenage entrepreneurs who showed up at an April dinner in New York honoring the 25th anniversary of the Network for Teaching Entrepreneurship (NFTE), a group dedicated to getting low-income kids interested in business. The thought of becoming a real entrepreneur can be thrilling for children accustomed to play money. But the reality is tough. Kids have to learn real responsibility and make sure they have insurance and pay taxes. NFTE (pronounced “nifty”) is there to help, from providing small start-up loans, to getting vendor licenses, to hosting 80-hour “mini-M.B.A.” classes in high schools that teach students about supply and demand, cost/benefit analysis, record-keeping, the present and future value of money, advertising and marketing, and working with suppliers. The value of its programs have been touted by entrepreneurs ranging from cosmetics creator Bobbi Brown to Internet pioneer Steve Case to rap artist Sean Combs.