SAN FRANCISCO — In the biggest moments on the baseball field, Buster Posey is unflappable as it gets. But he couldn’t keep from breaking down Wednesday while discussing a cause very near and dear to his heart.

Posey and his wife Kristen held a press conference at AT&T Park to announce plans to make pediatric cancer a primary focus of their philanthropic efforts. The Poseys, with the help of the Giants and New Era, are working to raise awareness and funds for pediatric cancer research and treatment.

Buster said this became a focus for his family when Kristen met a family who has a son, Cannon, who is only four days older than the couple’s twins but is fighting cancer. Buster had tears in his eyes as he spoke of Cannon and his discovery that only four percent of cancer funds raised throughout the country are dedicated to pediatric cancer research.

“It goes back to having children of your own and the gut-wrenching feeling you get thinking of kids (going through) something like that,” he said.

The new efforts are focused in three ways. New Era unveiled a Buster Posey Pediatric Cancer Awareness cap that has the Giants logo on the front, Posey’s initials and numbers on the back, and a gold ribbon for Pediatric Cancer Awareness on the side. Posey said 28 percent of the proceeds will go to support pediatric research and treatment.

The fundraising portion also includes an event on Sept. 14 with proceeds benefitting The V Foundation and pediatric cancer programs in the Bay Area. Dick Vitale, an ESPN college basketball analyst and longtime advocate for pediatric cancer support, will be the host.

The Poseys are also working toward increased awareness, and they’ll host Pediatric Cancer Awareness Day at AT&T Park on Sept. 17. Posey said Cannon, who is four years old, is scheduled to get his last dose of chemo the day of that event.

The third aspect of this increased effort is patient and family support, and the Poseys hosted several families on the field during batting practice Wednesday. Once per month, families will be invited to attend a Giants game and meet players and the Poseys on the field.

Posey said the goal is to provide as much financial support as possible going forward, starting with the sale of the special caps. He said repeatedly that this push “does mean a lot to me,” and he’s hopeful that his family can make a difference.

“We said we’ve got to do something,” he said. “We can’t talk about how bad this is. We’ve got to try to help.”