The victim, "just wanted a father figure," McGettigan said, "but the defendant would spoon with him, put his hand down his pants, touch his genitals."
Dottie Sandusky and her son, Matt, were escorted from their seats in the courtroom this morning to be sequestered with other witnesses. Other members of Sandusky's family remained in the courtroom.
A white tent was erected at the court's side entrance where the witnesses are expected to arrive, in order to protect them from the media and the public. Still, the alleged victims' identities will be made public for the first time when they take the stand to testify and their names are read into the public record. ABC News does not report the names of victims of sex crimes.
McGettigan also promised during opening statements to use Sandusky's own media interviews against him in court, noting that the jury would hear Sandusky's responses on NBC and in the New York Times to questions about his alleged crimes, prompting Amendola to confer with his paralegal.
The court took a break ahead of the first witness being called.
The investigation began in 2008 when a high school student in Centre County, Pa., told his mother and school administrators that Sandusky had molested him, launching a widespread but secretive effort to interview dozens of boys Sandusky mentored through his charity, The Second Mile, as well as Penn State officials who may have seen or heard about inappropriate actions.
Charges of child sex abuse were brought against Sandusky on Nov. 4, 2011, igniting a firestorm of scandal around the prestigious football program that led to the dismissal of the university's president and Paterno, and criminal charges against two school officials.
ABC News' Lauren Pearle and Candace Smith contributed to this report