There isn't much on South Beach to interest eight-year-olds. Nor is there anything constructive for your teenager to do. What to do then with the young ones when you're hankering for adults-only strolling, shopping, or lunching? The answer lies at the Scott Rakow center. It is a virtual summer camp where, for only three dollars on weekdays or six dollars on weekends (half price for Beach residents), fourth- to twelfth-graders can frolic. Among the diversions: ice-skating, swimming, bowling, basketball, and Ping-Pong. Qualified counselors provide supervision. On Sunday children of any age (including those over eighteen) can enjoy the activities. Hours are weekdays from 2:30 till 7:30 p.m.; Saturdays from 9:00 a.m. till 7:00 p.m., and Sundays from 11:00 a.m. till 7:00 p.m. A warning: Convincing the kids to leave may be difficult.