Some families do seem to be catching on to these possibilities. At Charles Schwab, 87 percent of all custodial accounts are Roths. Vanguard reports that about 2 percent of Roth I.R.A. contributors over the last five years have been people younger than 20. According to Fidelity, the number of Roth I.R.A. accounts there owned by people under 20 increased 22 percent from the second quarter of 2013 to the second quarter of 2014.

To parents who can’t simply write checks for college tuition, another car or an allowance, matching or even saving a teenager’s earnings in a Roth will probably seem highfalutin. If you fear that every dollar a teenager saves will lead to a need to borrow that much more money for college tuition, then it will be tempting to forgo the potential long-term winnings to keep the shorter-term loan balances as low as possible.

Image Credit... Robert Neubecker

Other parents may worry about the financial aid implications, given that colleges generally want families to turn over a large chunk of student assets each year. The good news here is that when you’re filling out the Fafsa form to determine eligibility for various forms of federal financial aid, a student’s Roth or other retirement account is not part of the calculation.

Scores of colleges and universities do require families to fill out an additional form known as the CSS/Financial Aid Profile. On it, student applicants must report a single total for all their retirement balances as of the end of the previous year. In theory, these schools could take this number into account when determining how much of their own grant money to award the applicant.

But for now, few, if any, colleges appear to be penalizing students for owning a Roth. Eileen O’Leary, assistant vice president for student financial assistance at Stonehill College in Easton, Mass., said she had seen a financial aid applicant disclose a retirement account only once. As far as she knows, asking students to pay more based on any such balance is not widespread. It may well be that so far at least, it’s mostly affluent families (who don’t need aid) who help their teenagers open Roths. Still, she suggests asking about a college’s policy if a financial aid applicant has a Roth or is thinking about opening one.

Kal Chany, who advises families through his firm Campus Consultants in New York City, has had only a handful of college applicants as clients who also had retirement accounts. Even though some of them have had balances upward of $10,000, he knows of no adverse impact on financial aid so far. Still, he said he feared that might change if lots of families started putting their children’s earnings in Roths or matched those earnings with their own money.