I advise all stay-at-home parents to have a side job in the event that their spouse dies and they have to re-enter the workforce, or a divorce happens (not unlikely but it happens).
Thus, I would see about the job market in your geographic area and look at what's in demand versus what your interests are and see where they intersect.
There are a variety of tools to help you find vocational interests:
- Public library: ask the librarian who specializes in their vocational guidance resources to advise you on their collection on picking a field of study and general career development strategies.
- Use your government's resources on labor projections or job market conditions to see what the outlook is on certain jobs or job categories.
- See if your local colleges have short term courses on career development. Coursera.org has one but its part of their MBA program.
- Some US-based tools are listed here.