RIDE THE STOCK MARKET WITH TRAINING WHEELS

Know someone with only $50 to invest? Mobile app Stash offers fractional purchases of stocks, and Acorns, a “round-up” app, moves extra pennies from credit- and debit-card purchases into ETFs. No-fee, no-minimum custodial Roth IRAs are available from both Schwab and Fidelity for youngsters with earned income. Roths grow tax-free for retirement, and original contributions can be taken out without penalty or tax at any time. A word of warning, though: Don’t try this if your kid might qualify for need-based aid from a private college.