A JPMorgan-backed personal finance app catering to children has doubled users this year. Now it's eyeing ways to let kids play the stock market.

· Greenlight, the personal financial management app for kids and parents, has seen its user base double since the start of the year.
· With this growth, Greenlight is building an investing product, where kids can propose stock and ETF trades to their parents.
· "To build true wealth, you really need to learn how to invest,"...