The House approved the measure 62-36, according to The Huffington Post. It's sponsored by state Rep. Jack Highfill (R) and now moves to the state Senate.
Current law doesn't allow anyone younger than 14 years old to handle firearms.
State Rep. Kirsten Running-Marquardt (D) fought against the measure.
"What this bill does, the bill before us, allows for 1-year-olds, 2-year-olds, 3-year-olds, 4-year-olds to operate handguns," she told local television station KCCI. "We do not need a militia of toddlers. We do not have handguns that I am aware of that fit the hands of a 1- or 2-year-old."
Highfill told the Washington Post that the criticism was unfounded because the bill includes language that requires parental supervision with "visual and verbal contact at all times with the supervised person."
“Allowing people to learn at a young age the respect that a gun commands is one of the most important things you can do,” he told the newspaper.
He added that otherwise, Iowans would turn 18 years of age "with no experience" in proper gun safety.
The law does not change the minimum age to purchase weapons.