With an image of Cesar Chavez smiling down on them, a group of Oakland kids rolled up and down a pristine half-pipe in a skateboard park that opened on Monday, the late farmworker activist’s birthday.

Now a state holiday, Cesar Chavez Day meant no school – and a chance to try an ollie or slide over a grind box in a neighborhood where brand new things don’t come around very often.

More than 200 volunteers showed up Saturday to build the skate park in one day on a former tennis court behind Rainbow Community Center in East Oakland. They also painted a mural of Chavez, which overlooks the park.

"Cesar Chavez would get people to do things for other people for free to show that he really cared about them," said Juvonna Jordan, 11, who wobbled on her first skateboard ride.

"A lot of bad things happen in Oakland, but this shows that some people can be nice," she said.

The skate park is among 10 playgrounds that are being built in needy California neighborhoods this year to honor Chavez’s legacy, with backing from the state agency CaliforniaVolunteers, which coordinates the annual Cesar Chavez Day of Service and Learning, and KaBOOM! a national nonprofit in Washington, D.C., that works to put playgrounds in struggling communities. Oakland City Hall also pitched in.

"They built this for Cesar Chavez, and for us, so kids won’t be on the corners dealing dope and going to jail or breaking into houses," said Billy Nivins, 11, who helped design the park.

When recreation leader Michael Lenzy opened the skate park at noon, more than a dozen youngsters were waiting to get in. Among them was Nivins.

"I’m going to stay until it closes, at 7:30," he said, grinning at his work.

If they weren’t skating, many of the children said they’d be indoors playing video games. Their neighborhoods are dangerous, they said, because drug dealers have taken over the corners. They also have to watch out for impromptu sideshows, the huge rallies where crowds watch drivers spin their cars in the intersections.

Lenzy said the kids aren’t making up stories. Last year, Rainbow Community Center workers found a woman’s body in the flood canal behind the center.

After a frenzied two-month planning period and marathon building session, Lenzy said he felt like he was floating as he watched children squeal with glee inside the skate park. He couldn’t stop grinning – until he saw some worn paint on one of the green benches.

"Hey! I don’t want to see this, you can’t grind on the bench! That’s what the grind box is for!"

Several boys apologized.

Right now, there are not enough skateboards to go around, but the children were pretty good at sharing, waiting their turns atop the half-pipe.

They had varying degrees of understanding of Chavez’s work to unionize California farm workers, but did realize he must have been a good man to warrant them a day off of school.

In 2000, California became the first state to establish an official state holiday in honor of Chavez. Other states, including Texas and Arizona, followed.

Today, congressional Democrats, led by the Hispanic Caucus, are expected to renew their call for a federal holiday for Chavez. They have been pushing since he died in 1993.

In Oakland, the kids were pushing for a mural showing Chavez on a skateboard, but they got overruled.

He smiles down on them with the United Farm Workers’ Aztec eagle symbol behind him.

"It’s still good," said Marlon Lee, 12, as he set up for another pass down the quarter-pipe.

E-mail Meredith May at mmay@sfchronicle.com.