A group of former Facebook and Google employees last week began a campaign to change the tech companies they had a hand in creating. The initiative, called Truth About Tech, aims to push these companies to make their products less addictive for children — and it’s a good start.

But there’s more to the problem. If you think middle-class children are being harmed by too much screen time, just consider how much greater the damage is to minority and disadvantaged kids, who spend much more time in front of screens.

According to a 2011 study by researchers at Northwestern University, minority children watch 50 percent more TV than their white peers, and they use computers for up to one and a half hours longer each day. White children spend eight hours and 36 minutes looking at a screen every day, according to a survey by the Kaiser Family Foundation, while black and Hispanic children spend 13 hours.

While some parents in more dangerous neighborhoods understandably think that screen time is safer than playing outside, the deleterious effects of too much screen time are abundantly clear. Screen time has a negative effect on children’s ability to understand nonverbal emotional cues; it is linked to higher rates of mental illness, including depression; and it heightens the risk for obesity.