Suffolk, England - For parents Daisy Greenwell and Joe Riory, freedom means looking up at the world around them instead of down at their phones, and they're determined to pass that sense of non-digital liberty on to their children.

Their daughter started asking for a smartphone when she was just eight years old, because her classmates were getting them. The pressure to have a phone at such a young age surprised Greenwell, and pushed her to look more closely at the trend.

She found a growing body of research suggesting that heavy smartphone use may negatively impact young people's mental health. 

The more she read, the more concerned she became, so Greenwell decided to take action. She posted a question on Instagram: What if we could switch the norm? What if parents united to create a "smartphone-free childhood?"

The response was immediate.

"That post went viral," she told CBS News. "Thousands of parents joined the group overnight."

Within a couple weeks, Greenwell said there were smartphone-free childhood groups in every county in England. One year later, the grassroots campaign has expanded far beyond the U.K. borders. 

The group — Smartphone Free Childhood — now has chapters in 39 countries.

For Greenwell, Riory and the thousands of families who've joined the movement, the goal is simple: More time outdoors, and a childhood lived offline as much as possible.  

In the U.S., the movement even inspired a cautionary viral advertisement, highlighting the dangers of giving children unrestricted access to the internet. A parent in the ad tells their child: "There's a box in the corner with all the pornographic material ever made. I'm trusting you not to look in there, okay?"

The backlash against youth consumption of social media has drawn the attention of governments globally. On Wednesday, Australia became the first country in the world to enact a ban on social media accounts for children under the age of 16. The law compels huge tech companies such as Meta and TikTok to enforce age restrictions, or face hefty fines. 

In the U.K., national Culture Minister Lisa Nandy said the government would be keeping a "close eye" on Australia's social media ban, but added that there were no current plans to replicate the legislation.

At a grassroots level, however, parents who join Greenwell and Riory's movement are asked to sign a pact: No smartphones for the kids before they turn 14, and no social media before 16.

"This isn't an anti-tech movement, it's a pro-childhood movement. We're not saying no smartphones ever. We're just saying children don't need unrestricted internet access in their pockets 24/7," Riory told CBS News. 

When asked what she'd tell busy working parents who rely on phones for convenience, Greenwell acknowledged the challenge. 

"It's really tough," she said. "But delaying the smartphone is free, it's simple, and it gives your child the best chance to thrive."

Many families are turning to basic "brick phones" as alternatives — devices that allow calls and texts, but limit internet access. Sales of such "dumb" devices have risen 150% among 18-24 year olds in the United States, according to a study by the peer-reviewed journal Partners Universal Innovative Research Publication.

Despite the momentum, Greenwell says there's still a cultural norm to disrupt, and available data highlights that point. One in four British kids between the ages of 5 and 7 already own a smartphone, according to the U.K.'s independent media regulator Ofcom.

Greenwell said she believes real change can be driven from the community level. 

"If children know several classmates are also delaying smartphones, the peer pressure dissolves," she told CBS News. "It becomes easier for families to wait a few years. A brick phone in the meantime isn't that hard. We can do this."