It's one huge perk of working from home. Lying down for 20 minutes makes the rest of the day much more pleasant and productive.
Check the CO2 levels in your office. They can get ridiculously high indoors when humans gather in the same room. It's not dangerous, but it makes people tired, they stop taking initiative, and less creative.
The natural rest position of the human eye is to focus at the infinite. Focusing on closer objects like books or screens requires a constant effort (we don't feel it).
The eye simply adapts and elongate to relieve some of the strain. Wearing corrective lenses further amplify the process.
If you want your kids to have perfect vision they should spend a lot of time playing outside, until early adulthood.
Clearly there's some significant environmental factor, and constantly focusing at short distances and/or getting no bright light exposure are the two obvious candidates (in other words, being inside all the time)
Whatever we're doing that isn't what they're doing is not normal.