Smartphone addiction among children is a concern, and not just for consumers. In an open letter, two major Apple investors are calling on the firm to address the issue of mobile device use among the young, and the effects it can have on their mental health.

Hedge fund Jana Partners and California State Teachers' Retirement System (CalSTRS) hold about $2 billion in Apple shares between them. While this represents less than 1 percent of Apple's total shares, they believe that the company's reputation, and therefore its stock, could take a hammering if nothing is done about the problem.

The letter cites a study carried out by the Center on Media and Child Health and the University of Alberta. It found 67 percent of more than 2300 teachers believe students are becoming even more distracted by digital technologies in the classroom.

Additionally, In the past 3 to 5 years since these technologies entered schools, 90% stated that the number of students with emotional challenges has increased and 86% said the number with social challenges has increased.

The research also shows that 8th graders who are heavy users of social media are more likely to suffer from depression, while those who spend an excessive amount of time on electronic devices are more likely to have a risk factor for suicide.

"The average American teenager who uses a smartphone receives her first phone at age 10 and spends over 4.5 hours a day on it (excluding texting and talking). 78% of teens check their phones at least hourly and 50% report feeling "addicted" to their phones," states the letter.

CalSTRS and Jana say parents' options are currently limited to an all or nothing approach of "shutting down or allowing full access to various tools and functions." They are calling for new tools and options, the forming of an expert committee that includes child development specialists, education for parents, and for Apple to release annual progress reports as it does for environment issues.

As one of the most innovative companies in the history of technology, Apple can play a defining role in signaling to the industry that paying special attention to the health and development of the next generation is both good business and the right thing to do.

Apple has not responded to the letter.