IT'S MIDDAY on the Mall, and the kids are overheating. If you're at the Capitol end of the culture trail, there's a midsummer's dream of a cool escape nearby in the Great Hall of the Folger Shakespeare Library. A free exhibit of 55 of the Folger's favorite things, marking the library's 55th anniversary, is on view till the middle of August and the Folger folks have put together a young people's guide to the show.

Kids can pick up the guide from a table just inside the arched stone entrance to the lofty Great Hall, itself a storybook castle hall with candelbra, carved oak paneling and intricate plaster ceiling. It's a question-and-answer sheet that directs young visitors to exhibits with special appeal to kids. Most of them will readily identify with the young King Henry VIII who scribbled "Thys boke is myne Prince Henry" in his 16th-century Cicero. And there are enough renderings of Shakespeare's visage -- in oils, print and marble -- to leave an indelible impression.

Also of particular interest for young students is the hand-size hornbook that 17th-century first-graders learned their ABCs from and the miniature nine-volume set of Shakespeare's works once owned by Charles Stratton, better known as General Tom Thumb, the three-foot star of P.T. Barnum's early 19th-century shows. There's also a detailed wood-and-thatch model of an Elizabethan theater.

And don't leave without a quick browse in the gift shop, where among the Shakespearean coloring books you can pick up a Frisbee inscribed "The Whirligig of Time" (from "Twelfth Night") or a kid's size T-shirt emblazoned with a spider and this quote from "The Taming of the Shrew": "Tush, Tush! Fear boys with BUGS." FOLGER'S CHOICE --

Through mid-August, in the Great Hall of the Folger Shakespeare Library, 201 East Capitol St. Open daily 10 to 4.