They are also learning a valuable skill (website development) which can be used to:
1- Sell domain names;
2- Find paid employment;
3- Help others, including through volunteering;
4- Keep up to date with technology;
5- Earn money from performance marketing;
6- Develop websites and sell them.
Well it can be depending if you now give them too many options on same niche or you can still do nothing active to sell domains. How hard is it to make a list then build around it? Those keywords might work.