VANCOUVER -- Parents should prioritize healthy habits such as physical fitness, nutrition and sleep over screen time long before kids reach their teenage years when arguments over devices can become a huge issue, says a doctor who leads the Canadian Pediatric Society's digital health task force.

Dr. Michelle Ponti said the society's new guidelines emphasize how and when screens are used based on age rather than prescriptive time limits when it comes to low and moderate exposure to electronic devices.

"We're trying to avoid the fights by starting these screen-time limits and these digital literacy talks with families early," said Ponti, a London, Ont., pediatrician who has a nine-year-old son and two teenage daughters, aged 17 and 18.

"It's much more difficult to pull back with a teenager," she said, adding excessive, isolated and passive use of screens, especially if they are allowed in youngsters' bedrooms, can be most harmful for kids and adolescents.

Research suggests five or six hours a day of screen use is excessive but it's important to put that in context depending on whether that's happening during the week or on weekends and whether kids are using computers to do homework, Ponti said, adding the different needs of children within a family should also be considered when monitoring online activities.

"My oldest daughter is quite responsible with her phone, my middle daughter, I have to constantly remind of screen-time rules and my son, he doesn't even own his own mobile device but he has access to the family's computer and the television and he has a gaming system," she said.

For children aged five to 12, the society recommends families watch educational programming together, focusing on content that promotes positive social skills, adding that heavy screen use during those ages appears to be linked to negative outcomes such as depression.

The time to start having conversations about screen time and setting rules is when kids are in pre-school and also to model good behaviour, such as not texting while driving, Ponti said.

"We really want families, kids and teens to have these conversations about how screens can fit into their lives in a productive way rather than detracting from all the other healthy habits we're hoping they've already prioritized. Have these conversations, honestly and openly with teens and do it at a time when there's not a fight."

Teachers are also increasingly finding students' use of phones in the classroom a big distraction that can interfere with learning so schools are in the same position as parents when it comes to conflict over screens, Ponti noted.

"And physicians are finding that this has been a kind of runaway train over the last five, 10 years and now we're trying to rein it back in and set some guidelines, policy and rules."

Cellphones will be banned in Ontario classrooms starting in September, and jurisdictions around the country have various rules in place to deal with the devices while individual teachers decide the rules in some schools.

"We also, as pediatricians, need to support the educators advocate for healthy use of screens," Ponti said. "We know (screens) can enhance learning but the teens are looking at their social media profiles and Snapchatting their friends in the classroom."