"It looked like they were doing a car for a minute," her father, Jonathan, said with a laugh.
Khalilah Lawson said the family had been drawn from its home near the airport to the carnival.
"I work here in the city, and I heard about this," she said, adding that the family would be attending other events during the 10-day festival.
"We're getting a little science," she said. "This is great!"
Throngs wore stickers that read "I love science" or "I am a scientist." And the size of the crowd swelled as cloudy skies gave way to sunshine, and a steady breeze sent pylons of green, white, and black balloons dancing on a glorious April day.
More than 130 activities and performances beckoned, including a bubble-making station, chances to clamber aboard a small red helicopter, and opportunities to observe science demonstrations of all kinds.
Sarah Johnstone of Blue Bell, a graduate student studying neuroscience at Penn, was part of a large group spending the day at the carnival.
"We're a family of scientists," explained Johnstone as Annika Khavin, 5, a family friend, plucked a red cork that had landed at her feet during an explosive segment in a "Mad Science" show.
Kimberly Brooks of South Philadelphia snapped photos as daughters Angel, 10, and Cierra, 9, turned a big, blue wheel to power a small-scale wind turbine.
She said her daughters' science teacher at Folk Arts Charter School on Callowhill Street had encouraged them to attend.
The girls said the turbine was fun and so was a Philadelphia University exhibit where stepping onto a chemical mixture had made them feel as if they were walking on water.
Science interpreters from the Franklin Institute delighted crowds with noisy, combustive demonstrations that produced clouds, fireballs, and explosions.
"It's great to see so many people interested in science," said Adrienne Kimball, who runs the institute's summer camp. "What we really try to do is inspire that curiosity."
Science interpreter Buddy Muhler, who had dyed part of his beard green for the day's wacky routines, added: "We try and throw education content in there, but we don't expect people to remember all of it. Even if they remember that one little nugget they thought was really fun, we consider our job has been done."
Produced by more than 105 partners with principal sponsor Dow Chemical Co., the festival's theme is "Feed Your Curiosity."
It continues with events across the region through next Sunday.
Contact Martha Woodall at 215-854-2789 or firstname.lastname@example.org.
For information on other festival events in the Philadelphia area, go to www.philasciencefestival.org.