Even hedge fund moguls think kids are spending too much time on their iPhones.

Barry Rosenstein’s Jana Partners, together with the California State Teachers’ Retirement System, are going after Apple — urging the tech titan to develop software to allow parents to more easily limit the amount of time kids spend on their iPhones, according to a letter the two investors sent the Cupertino, Calif., company on Saturday.

“We believe there is a clear need for Apple to offer parents more choices and tools to help them ensure that young consumers are using your products in an optimal manner,” said the letter, which was made available on thinkdifferentlyaboutkids.com.

“There is a developing consensus around the world including Silicon Valley that the potential long-term consequences of new technologies need to be factored in at the outset…,” the letter added. The letter was first reported by the Wall Street Journal.

Jana and Calstrs, which together have a roughly $2 billion stake in the $900 billion company, also want Apple to study the effects of cellphone use on kids.

Apple is just one Silicon Valley-based company facing increased scrutiny over the potential harms of its technology. Facebook CEO Mark Zuckerberg pledged to spend 2018 protecting its users from “abuse and hate, defending against interference by nation states, or making sure that time spent on Facebook is time well spent.”

Separately, Jana is raising money for a fund that will focus on socially responsible investing. Musician Sting and his wife, Trudie Styler, will sit on its board.

Reps from Apple and Calstrs did not respond to requests for comment.