Calvin Sprouse slid his finger across the iPhone screen.

A Lego robot responded by buzzing around the floor in front of him.

Calvin, 11, built the robot. And he has his sights set on building even bigger ones someday.

“I really like designing and programming robots, and Mars rovers have always interested me. I really want to do that,” he said.

Calvin shared his passion for robotics with other kids Saturday during the fifth annual Playdate Family Expo at the Yakima Convention Center. His dad, Paul Sprouse, owns the North Bend-based Valley Robotics, which provides science, technology, engineering and math (STEM) education through activities such as Lego robotics and computer programming.

Paul Sprouse was the resident Lego expert at the Playdate Expo, sponsored by the Yakima Herald-Republic. He said he was inspired to start Valley Robotics by his son’s NASA goal, and his mission is to inspire students to learn more about STEM fields — and to have fun along the way.

His booth Saturday was packed with kids of all ages. Some built Lego houses, castles or even horse corrals, while others tested the Lego robots and motorized Lego tanks, or got a glimpse of the kinds of computer programs they could learn to design.

The Playdate Family Expo drew more than 1,200 people last year, and organizer Shannon Hitchcock said she expected Saturday’s attendance to top 1,500 people.

“I just want families to have a good time,” said Hitchcock, the business development manager for the Herald-Republic.

About 45 vendors were on hand during the event.

Jose Gaxiola, 15, a sophomore at Toppenish High School, volunteered to help Sprouse at the booth. He said he’s interested in engineering, especially after seeing what the Lego creations could do.

“I like to see how things work,” he said as he tested out a Lego tank.

Alex Alcala Jr., 6, of Yakima seemed fascinated by the Lego booth, too. He bounced from building a Lego structure to taking one of the robots for a spin using Calvin Sprouse’s phone.

Trevor Mayhak, 7, of Naches focused on building a Lego ship. He said he likes playing with the colorful blocks because, “You can make anything you want.”

Paul Sprouse, meanwhile, showed off the Lego robots and tanks and answered questions from kids and parents. STEM education is important, and throwing in Lego toys and robots makes the learning more fun, he said.

One Yakima boy seemed to be getting that message.

Adrian Town, 7, worked intently in Sprouse’s booth to build a Lego castle.

“You can make really cool things,” he said with a smile. “I like that you can build and your imagination tells you what it wants. And you have fun.”

• Reporter Susana Torres, a junior at Zillah High School, and photographer Ariana Velazquez, a senior at Eisenhower High School, participated in the “2014 Valley Workshop: Stories in Your Backyard” at the Yakima Herald-Republic on Friday and Saturday.