Bob Pack was doing what dads do: watching football on a late Sunday afternoon. His kids, Troy, 10, and Alana, 7, were doing what kids do: short-circuiting their father’s best-laid plans.

So Pack did what really cool dads do.

“The kids were getting rambunctious and making a lot of noise,” recalled Carmen Pack, Bob’s wife. “He suggested we go out for ice cream.”

The Pack family and a couple friends of their kids headed west on Camino Tassajara in Danville. In the blink of an eye, the Rockwellian tableau turned to unspeakable horror.

“They were on their bikes and scooters, and two of their friends were along,”  Carmen Pack said. “You never, ever imagine a car going on the sidewalk. The kids were wearing helmets, being very safe, waiting for the light to change to green. We walked together, and as soon as we started walking, the car just came right on all of us. It was incredible. I had nightmares for many years.”

Troy and Alana were killed on that October evening in 2003. Tuesday evening, the Packs returned to the scene of the tragedy at Camino Tassajara and Rassani Drive. In truth, they’ve never really left. They still live just down the street with their daughter Noelle, born three years after the accident. Bob Pack says he passes the site almost daily.

“It’s only half a mile up the road,” he said. “I think about it often. Why couldn’t it be different? What could have changed?”

This time it was a little different. This time there was a hint of sweet to go with the bitter. Earlier Tuesday, Pack, 61, received a call from Sacramento. A bill he advocated and championed, aimed at thwarting patients from stockpiling dangerous drugs, as did the woman who killed his kids, had been signed by Gov. Jerry Brown.

The law, which takes effect Jan. 1, requires doctors to check a database for a patient’s prescription history before prescribing opioids and other potentially dangerous drugs.

“It has been a long road,” he said. “It’s been 13 years since I lost my children. It’s been at least 10 or 11 years that I’ve been working on this prescription drug issue.”

It took a few years for Pack to identify and embrace the issue. In turn, the issue enabled Pack to segue, somewhat, from pure grief to proactivity.

“I was totally green to politics,” he said with a chuckle. “Maybe it was a good thing. I jumped in feet first and yes, it was a long and very exhausting road because you have so many interest groups and lobbying groups and special interests and political alliances, and those are very hard to overcome.”

A bill nearly identical to the one signed Tuesday was defeated in 2012. “I really thought that could be the end,” Pack said.

It was a fleeting thought.

“I remember clearly him telling me, ‘I’m not quitting,’” Carmen Pack said. “He’s a very persistent person and has a lot of determination.”

As Pack educated himself on what he calls “the political spectrum,” he found that his new mission had therapeutic value.

“Very much, because I like to be active, doing things and busy,” he said. “And that makes me feel good. So yes, this has been a 10-year path of therapy for me by keeping this going.”

He sees other opportunities for advocacy related to the prescription drug issue. But that’s for later. Tuesday was a time for reflection. As Bob Pack spoke to the couple dozen or so friends at the site of his worst nightmare, straining to be heard over the traffic roaring past, it was evident he is still the cool dad — not only to his daughter Noelle, but to Troy and Alana, whose memories he continues to serve.

“I can’t help but feel had this bill been implemented 13 or so years ago, my children would be here today,” Carmen Pack said. “But on the other hand, only God knows how many lives this bill is going to save. It’s a good feeling. Today is a good day.”