There's new evidence that "parental control" button on the America Online and Prodigy dial-up services may more important than some parents thought. The Vienna, Va.-based America Online has announced that the FBI is investigating a "small number of people" who have used the system's E-mail to transmit child pornography, after about a dozen AOL members who received the dirty pictures recently lodged complaints. AOL president Steve Case said that AOL contacted the FBI and terminated the individual accounts as soon as it learned of the abuses.Of special concern is the threat that some users may prey on young children who use online services without their parent's supervision. In New York today, WCBS Radio reported that a concerned Westchester County father, George Telesha, was sent pornographic messages and pictures after he entered one of AOL's racy "chat rooms" pretending to be a 14-year-old girl named "Susie." The incidents were the latest in a series of porn-related problems for online services and the Internet: last month, a California couple was jailed for allowing "obscene" photos on their bulletin board service. Pam McGraw, an AOL spokeswoman, told TIME Daily the service advises parents to use the "parental control" feature to keep children from entering certain "chat areas" and from receiving one-on-one "instant" messages.