Investors are issuing a warning to tech giant Apple to curb its smartphone marketing strategy amid fears the iPhone is a mental health hazard to children.

Activist investors Jana Partners LLC and the California State Teachers’ Retirement System, which own about $2 billion worth of Apple stock combined, expressed their concerns in an open letter, saying the iPhone is designed to be “as addictive and time-consuming as possible.”

DivaMoms CEO Lyss Stern told FOX Business’ Neil Cavuto Monday that the excessive use of smartphones among children is what keeps parents up at night.

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