It’s not Apple or CEO Tim Cook‘s responsibility to parent kids’ iPhone use, CNBC’s Jim Cramer said Monday.

Cramer spoke after two major Apple shareholders, Jana Partners and the California State Teachers’ Retirement System, urged the tech giant to take steps to address what they say is a growing problem of young people getting addicted to iPhones.

Jana and CalSTRS combined control around $2 billion worth of Apple shares, according to The Wall Street Journal.

Cramer said he was surprised the shareholders didn’t suggest that Apple ask parents to take a greater role in their kids’ smartphone usage. Apple hasn’t offered guidance on how parents should manage their kids’ phone use.

“Is that Tim Cook’s job to get the parent’s involved? I don’t think so,” said Cramer, whose charitable trust owns shares of Apple. But Cramer added he did believe this was an important issue.

“The prevailing wisdom in the mental health community … in this country is the parents aren’t playing a big enough role,” Cramer said on “Squawk on the Street.” “It is not the institutions. It is not the kids. It’s the parents. And I thought that was a very interesting lack of understanding about what the prevailing wisdom in mental health is.”

“It’s not like Tim Cook is saying ‘We’ve got to get these in the hands of underage,'” Cramer added.

The shareholders reportedly cited surveys and studies on how excessive smartphone usage and social media negatively impact kids’ mental health.

Many health experts agree that excessive smartphone usage does have an impact on adolescents and their mental health. Though there is some debate on the best approach to deal with the matter.

According to a 2016 survey by Common Sense Media, half of teenagers in the U.S. feel like they are addicted to their mobile phones.

Apple did not immediately respond to a request for comment on the letter.

— Reuters contributed to this report.