A pair of big Apple investors are urging the iPhone maker to do more to tackle the issue of smartphone addiction amongst young people.

Jana Partners, an investment manager, and The California State Teachers’ Retirement System (CalSTRS), an educator-only pension fund, delivered an open letter to the tech giant over the weekend calling on the tech giant to consider developing software that would help parents to limit the smartphone use of their children.

The pair, which hold around $2bn in Apple shares combined, also ask that Apple conducts research into the impact that excessive phone use can have on mental health. They reference several previous studies that have found there to be a range of negative consequences as a result of the amount of time young people are spending on mobile devices.

“We have reviewed the evidence and 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,” reads the letter signed by Barry Rosenstein, managing partner at Jana, and Anne Sheehan, director of corporate governance at CalSTRS. “… Apple’s current limited set of parental controls in fact dictate a more binary, all or nothing approach, with parental options limited largely to shutting down or allowing full access to various tools and functions.”