The bill would also ban so-called nudging techniques designed to subtly get children to allow data sharing, as well as collecting data including location information for purposes outside of the product or service the child is using.

“I come to this bill not only as a legislator but as a mom of a five-year-old little girl who is familiar with technology, and we try to curate her experience as much as we possibly can, but it’s hard for parents to do this,” Ms. Wicks said. “I think it’s time that the tech companies play a more proactive role in helping to ensure that there are guardrails to keep our kids safe.”

The bill comes as legislators and regulators around the world are increasing pressure on social media companies over their interactions with users under the age of 18, a response to growing questions about how social media affects its users, and particularly children.

U.S. Sens.

Richard Blumenthal

(D., Conn.) and

Marsha Blackburn

(R., Tenn.) on Wednesday proposed federal legislation that would hold social media companies responsible for harm they cause to children. Their bipartisan Kids Online Safety Act would also require tech companies to periodically assess how their algorithms, design features and targeted advertising might cause harm to minors.

Technology companies say they take children’s safety and privacy seriously. Some, including

Alphabet Inc.’s

Google and

Meta Platforms Inc.’s

Messenger, have created products specifically for people under 18 to minimize interaction with adult content, and have rolled out their own safety tools, without regulatory prompt.

Additionally, several social media companies modified their children’s user experience in the year before the British government began enforcing the Children’s Code in September 2021, implementing some changes globally.

Google made SafeSearch the default browsing mode for all users under 18, turned off YouTube autoplay by default for the same group and blocked ad targeting based on the age, gender, or interests of users under 18. TikTok, meanwhile, stopped sending push notifications after 9 p.m. to children age 15 and younger, and after 10 p.m. to 16- and 17-year-olds. Neither company at the time said they made these changes in response to the code’s introduction.

The politicians and advocacy groups behind the U.K.’s Children’s Code have had conversations on the subject with U.S. lawmakers at the state and federal level, said

Beeban Kidron,

a peer in the U.K.’s House of Lords and architect of the U.K. regulation.

If passed, the California bill will carry particular weight given the number of technology companies based in the state, she said.

California’s existing privacy legislation, which is similar to the U.K.’s Data Protection Act, also means the state would be able to more easily absorb the code into law, Baroness Kidron said.

“We are seeing extraordinary focus on child protection across the U.S., but so far, bills in Congress have not made it to the statute books,” she said. “Should California, whose residents already enjoy greater privacy protections, be able to additionally protect kids, then it will galvanize others.”

Ms. Wicks last year introduced a similar bill designed to better protect children online, but it failed to pass. The new bill comes with Republican support and is intended to act more as a set of instructions for the California Privacy Protection Agency, which only began to take shape toward the end of last year, she said.

She said she expects the California Age-Appropriate Design Code Act to begin the committee process in the spring, and anticipates “robust conversation with the tech companies.”

“We know that tech companies can do it, because they’re doing it in other places and it hasn’t negatively impacted their business models,” she said.

Write to Katie Deighton at katie.deighton@wsj.com