Barbara Park, whose children’s books starring Junie B. Jones, a 6-year-old dispenser of abundant opinions, Runyonesque wisecracks and dubious syntax, have sold tens of millions of copies and delighted all but the most grammatically puritanical parents and teachers, died on Friday at her home in Scottsdale, Ariz. She was 66.

The cause was ovarian cancer, her publisher, Random House Children’s Books, said.

Aimed at beginning readers and illustrated by Denise Brunkus, the Junie B. series comprises nearly 30 titles. The books have sold more than 55 million copies in North America, according to Random House, and have been translated into a dozen languages.

If almost any of Ginger Rogers’s tough-girl characters had been portrayed as a child, she would have been much like Junie B. In the very first book in the series, “Junie B. Jones and the Stupid Smelly Bus” (1992), Ms. Park’s young heroine bursts onto the page fully and irrepressibly formed:

“My name is Junie B. Jones,” she declares in the opening sentence. “The B stands for Beatrice. Except I don’t like Beatrice. I just like B and that’s all.”

At the start of the book, Junie is about to begin kindergarten, which, as she sagely observes, “is where you go to meet new friends and not watch TV.”