A Denver dad says smartphones turned his two youngest sons into zombies. So he turned himself into a crusader.

Timothy Farnum, an anesthesiologist, wants Colorado to be the first state to ban smartphone sales to children younger than 13, and he already has plenty of parents on board. The behavior of his boys, ages 10 and 11, underwent striking changes when they got phones.

They became withdrawn, distracted, disinterested in playing outdoors. When he tried to take the phones away, Farnum told CNN, one of his previously easygoing sons showed symptoms that looked alarmingly like drug withdrawal: “He was very addicted to this little machine. It kind of scared me.”

Parents face an everyday challenge in trying to sort out the rapid-fire changes mobile technology is making in American life. How much is too much? Does early mastery of technology give kids a competitive edge later on? If electronic content is labeled “educational,” does it help or hinder?

All valid questions, all slowly being sorted out by pediatric experts. Their short answer: Media are inescapable for children growing up today, and it’s up to parents to be careful and vigilant regulators.

Farnum’s initiative, which would require retailers to ask pointed questions of shoppers about who will use new phones and maintain exhaustive records, is a long shot, and he admits as much.

He hopes, he says, to at least get parents to examine current scientific studies on the effects of screen time on young children and teens to better enable them to set guidelines for their own families.

Such studies abound with cautionary messages: Excessive media exposure, especially for younger children, can interfere with sleep, hinder social development and discourage physical activity.

Being a parent is no easy business; runaway technology often rockets beyond the research.

But the research in this area is emerging with a consistent message: Too much mobile media exposure is a problem for our kids.