The toddler picked up the gun and pulled the trigger, police say, killing his mother.
Though the tragedy may seem shocking, it happens with alarming frequency. In the past week, at least five children across the country have found and fired handguns -- with deadly consequences.
In one case, a boy killed his mother. In other cases, the children kill themselves.
But the shootings aren't accidents, gun violence prevention activist Jonathan Hutson said.
"These fatalities are unintentional, but they're not accidental," said Hutson, former spokesman for the Brady Campaign to Prevent Gun Violence. "They're foreseeable and preventable."
Mother killed by son while driving
Price, 26, was driving her boyfriend's car along a Milwaukee highway Tuesday morning when the gun slid out from under the driver's seat and was picked up by her 2-year-old son.
The boy was in the back seat; Price's 1-year-old was in the front passenger seat, along with Price's mother, the Milwaukee County Sheriff's Office said.
It's not clear whether Price knew that her boyfriend, a security officer, had a loaded gun hidden under the driver's seat.
Price's aunt, Vonja Thomas, said her niece worked hard to take care of her two children. She said Price would never knowingly have a loaded gun near them.
"She tried to work two jobs. She would do anything for her kids," Thomas told WDJT. "If she knew, I'm sure she wouldn't have had a gun in that car. But that wasn't her car. That wasn't her gun."
One week, several shootings
The recent wave of fatal shootings by children spans the country.
9 children a day
At least 14 states and the District of Columbia have laws that make gun owners criminally liable if they fail to prevent unauthorized access to guns by children, according to the Law Center to Prevent Gun Violence.
But many children are still shot unintentionally, Hutson said. On average, he said, nine children under age 18 are unintentionally shot in the United States every day. Of those, about seven die each day. Hutson said those numbers have been fairly steady over the past few years.
Twenty-four children under age 4 died from accidental shootings in 2014, the most recent year of data available, according to the Centers for Disease Control and Prevention.
The data don't distinguish whether those children shot themselves by accident or were shot by someone else.
How to keep children safe with guns at home
He said it's up to a parent to decide when a child is physically able to hold a firearm and mentally prepared to understand its consequences.
"Teaching your kids how guns work and to understand what they do and what happens when they go off is very important," he said. "Kids have an incurable curiosity; that's the first thing that gets everyone in trouble. If you train a child, it takes the mystery away, so they know what it is and see what it does."
Hutson said responsible gun owners should keep their firearms locked in safes and store their ammunition separately when children are in the house. But that doesn't always happen.
"It's heartbreaking to know that these parents, like many of those in America, bring these guns into their homes thinking it'd make their homes safer," he said, "but they actually fail to store the gun and ammunition separately -- with tragic results."
CNN's John Bonifield, Emanuella Grinberg and Michael Pearson contributed to this report.
