[cagz]

Assuming they've got reasonable programming skills. They can simply find an open-source project they are passionate about. Spend time understanding the overall structure. Then pick up an issue raised by the community and prepare a fix as a pull request.

The first PR is unlikely to be merged the next day; however, it sparks lots of productive discussions with the rest of the community, allowing your kid to build a mental model of the project's best practices and sensitivities.

The more he contributes, the more integral he becomes to the community. After gaining enough experience through small issues, they can even consider working on a new feature.

As a byproduct, a great addition to the CV if they are also looking to go commercial.