Are kids who spend less time outdoors more likely to develop ADHD?

There's no strong evidence that time outdoors specifically prevents or causes ADHD, though this idea often gets mixed up with a different, more modest finding about symptom management. Some research suggests time in green outdoor space may modestly help with attention and mood generally, but that's a symptom-management observation, not evidence that too little outdoor time causes the underlying condition. ADHD's strong genetic basis means a child's risk is set well before outdoor time becomes a relevant daily factor. References: https://doi.org/10.1038/s41380-018-0070-0

I was an extremely outdoorsy kid, constantly outside, and still got diagnosed as an adult. Screen time and outdoor time never felt like the actual variable in my case. It really did feel like the transition itself was the driver, since her behaviour at home barely changed during that same stretch. A pretty clean natural experiment, in hindsight, even if we didn't plan it that way.