SAN DIEGO -- Hundreds of San Diego County children, many with delighted parents in tow, spent their Saturday celebrating science at Balboa Park.

"It's wonderful," Deepti Mahadevia of Poway said at the 2009 San Diego Science Festival. "The kids love it. They're thrilled to be here."

Her son Rahul Shaw, 13, an eighth-grader at Black Mountain Middle School in Poway, was building a paper rocket at one of more than 300 booths and interactive exhibits at the San Diego park.

"It's fun, and it's a good way to explore science," Rahul said.

Michelle Andrew of Encinitas was watching her sons, Jacob, 13, and Kellen, 9, extract DNA from what Jacob described as "squished" strawberries.

"I think it's great, there's a lot of hands-on stuff for them to do," Andrew said.

"Usually I don't like science, but this is fun because you actually get to experiment," said Kellen, a third-grader at Flora Vista Elementary School in Encinitas.

The festival created daylong traffic jams on streets leading to the park and long lines of children on the park's grounds waiting to steer underwater robotics equipment or launch handmade rockets.

They looked through microscopes, played brain games and steered remote-control miniature Mars rovers across red-tinted mounds of dirt.

"That's what we live for, getting the kids excited about Mars," said Gerry Williams of San Diego, a member of the Mars Society of San Diego County.

Jasmin Yoon, 16, and Parth Sitlani, 17, of Rancho Penasquitos, both students at Mt. Carmel High School, were at a booth handing out free comic books describing the dangers of polluting oceans.

"Anything toxic you throw out somehow ends up in the ocean," Sitlani said. "The kids are learning not to pollute. They get it."

The festival, sponsored by more than 100 science organizations, also featured free admission to Balboa Park's natural history, sports and science museums.

"The crazy thing is how many kids are here," said Kai Kuspa, 16, a junior at Canyon Crest Academy in Carmel Valley, who was working the Greater San Diego Science and Engineering Fair booth at the park.

Kuspa was showing youngsters how to create 30-foot geysers from dropping a handful of Mentos mint candies into two-liter plastic bottles of Diet Coca-Cola.

"The carbon dioxide is released, and then it fizzes up out of the only opening. A fountain will go 30 to 40 feet in the air," he said.

Lydia Zdeb, 15, a sophomore at Rancho Buena Vista High School in Vista volunteering with Kuspa, noted the equal mix of girls and boys crowding the festival.

Dozens of organizations "have been pushing for women in science" for several years, Zdeb said.

"It's working," she said about efforts to close the gender gap in a field still dominated by men.

"Girls are getting so much more encouragement at young ages and realizing that smart can also be attractive," Zdeb said.

Zdeb and Kuspa also were rooting for North County peers competing at the 55th annual Greater San Diego Science and Engineering Fair under way through Sunday at an activity center across the street from Balboa Park.

This year's winners have included North County students from Canyon Crest, Scripps Ranch, Carlsbad and Torrey Pines high schools.

For more information about the science and engineering fair results, visit www.gsdef.org.

To learn about year-round science events for children and grown-ups in San Diego County, visit www.mysdscience.com.