One of the hardest things for an adult actor to do is become a child onstage. Too often the result is more caricature than character, all toothy smiles and oversize pigtails and stomping feet. It's rare to find a performer who can not only master the physical gestures of a young person but also crawl inside her head as well.

Cathy Simpson has achieved such a feat in "Pretty Fire," a one-woman theater piece by Charlayne Woodard playing this weekend at the Lyceum in Alexandria and then at D.C.'s Source Theatre. Portraying Woodard as a girl of 5 or 8 or 11 (in addition to a host of other characters, mostly grown-ups), Simpson uses her formidable and versatile speaking and singing voice, her keen sense of timing and her slight, taffy-limbed frame to marvelous effect.

Woodard's effervescent memoir of growing up in the bosom of a loving African American clan in Albany, N.Y., circa 1960 is in large part written from the point of view of a rambunctious, show-biz-adoring child, and Simpson proves irresistible in a role that could easily veer toward the cutesy and contrived.

"I want to be Lassie!" young Charlayne responds when her mother asks what she wants to be when she grows up, and Simpson, suddenly collie-like, plays to the invisible camera. Sensing her mother's disapproval, she amends her answer to "I want to be Shirley Temple!" This affords the actress the chance to launch into an adorable little tap number alongside an invisible Bill Robinson.

There are stark and serious moments in which Simpson shines as well--a terrifying sexual assault by a neighborhood bully in which the actress conjures up both the grabber and the grabbed, and a night spent huddled with relatives down South as a cross burns on their front lawn. So evocative are both the script and the performance that you see those flames, that "pretty fire," though the actual set consists only of a big red armchair, and lighting effects are minimal. It's the child's crunched-up body, her inordinately wide eyes and ghost-story-style inflections that do it to you.

Simpson, who over the years has created some unforgettable but far less exuberant characters on area stages--a majestic Lena in Athol Fugard's "Boesman and Lena" at Metrostage, a brilliantly downtrodden Ruth in Olney's recent production of "A Raisin in the Sun"--does a fine job of impersonating the many diverse figures who inhabit young Charlayne's universe. Among the gems: her father's unrelenting and repetitive alphabet lessons, her grandma's "life lessons," a Jamaican nurse's reaction when she caught an eyeful of baby Charlayne just after her very premature birth; her grandfather's reaction to the suggestion that she be named "Africa" ("She don't have a hard enough time already? She a child, not a land mass!"). They are so beautifully written by Woodard, so lovingly fleshed out in all their glorious eccentricity by Simpson, that the stage seems populated by a whole feast of souls.

Pretty Fire, by Charlayne Woodard. Directed by Ceal Phelan. A Metrostage production; Carolyn Griffin, producing artistic director. June 12-14 at the Lyceum, 201 S. Washington St., Alexandria, and subsequent Sundays, Mondays and Tuesdays through June 30 at the Source Theatre. Call 703-548-9044.

CAPTION: Cathy Simpson captures the wonder and exuberance of girlhood in the one-woman show "Pretty Fire."