We can assume the two are so strongly correlated that it's not worth it to differentiate. Even though many exceptions exist.
They can, if they practice with feedback 8 hours a day.
Typically, young people, as a group, are not famous for practicing something 8 hours a day.
This means, for the group as a whole, it is true.
Children can work open source and rack up experience there. This is like the most humane way in any job ever to get experience as a minor.
While open source may be okay for coding, there are other skills which may not be so easy to do from your own home. In practice they will not just do open source and people will exploit them for free work