Opening your child's first investment account: a step-by-step guide to custodial index fund investing

You don't need a lot of money, a financial advisor, or a complicated strategy. Opening an investment account for your child takes about 20 minutes at Fidelity or Vanguard. Here's exactly what to do, what to buy, and what happens as the child grows up.

UTMA vs. UGMA: which account type?

Custodial brokerage accounts for minors come in two forms: UTMA (Uniform Transfers to Minors Act) and UGMA (Uniform Gifts to Minors Act). Both work the same way for practical purposes — a parent or grandparent opens and manages the account as custodian, and the assets transfer to the child at a specified age.

The differences are minor for most families:

• UTMA is available in most states and allows a broader range of assets (securities, real estate, patents, other property)
• UGMA is available in all states but historically restricted to securities only
• For a family investing in index funds, both work identically
• The transfer-to-child age is typically 18–21, but varies by state. UTMA allows some states to extend this to 25

For most parents, the recommendation is simple: open a UTMA custodial brokerage account at Fidelity or Vanguard and invest in a broad index fund.

Which brokerage: Fidelity vs. Vanguard

Fidelity is the easiest option for most parents. The online application is fast, there's no minimum to open, and you can invest in FZROX — the Fidelity ZERO Total Market Index Fund — which has a 0.00% expense ratio. Zero. The fund tracks the entire U.S. stock market. You cannot hold FZROX at any other brokerage (it's Fidelity-exclusive), but for a custodial account you intend to hold at Fidelity long-term, this is ideal.

Vanguard is equally strong. Their equivalent funds are VTSAX (admiral shares, $3,000 minimum) or VTI (ETF version, no minimum — buy in dollar amounts). Expense ratio: 0.03%. Vanguard's platform is slightly less modern than Fidelity's but has an excellent long-term reputation, and the Vanguard custodial account is widely used.

Either is a fine choice. Most new investors find Fidelity's interface simpler.

Step-by-step: opening a Fidelity custodial account

1. Go to fidelity.com and click "Open an Account"
2. Choose "Custodial Account" from the account type menu
3. Enter the custodian's information (your name, SSN, date of birth, address)
4. Enter the child's information (name, SSN, date of birth) — you will need their Social Security number
5. Link a bank account for funding and transfer your initial deposit (no minimum)
6. Once funded, search "FZROX" and select "Buy" — you can invest in dollar amounts, no need to buy whole shares

That's it. Total time: 15–20 minutes. The account will show the child's name and your name as custodian. You manage it until they reach the age of majority in your state.

What to buy: the case for one index fund

For a child's long-term investment account, the best first investment is almost always a total U.S. stock market index fund. This gives exposure to thousands of companies across every sector — the same fund that Warren Buffett famously recommended ordinary investors use.

• At Fidelity: FZROX (Fidelity ZERO Total Market Index Fund) — 0.00% expense ratio
• At Vanguard: VTI (Vanguard Total Stock Market ETF) — 0.03% expense ratio, or VTSAX if you have $3,000

The expense ratio matters over decades. A 0.5% fee on a $100,000 balance costs $500/year in lost compounding. A 0.03% fee costs $30. At 18 years, this difference is meaningful.

A real example: parent opens a Fidelity custodial account with $1,000 and buys FZROX. At 7% average annual return, that $1,000 becomes approximately $3,380 in 18 years — without any additional contributions. Add $100/month for 18 years and the total is approximately $48,000. See the full compound growth math here.

Tax implications: the kiddie tax

Investment income in a custodial account is taxed — this is different from a Roth IRA or 529. Here's how it works for 2026:

• For children under 19 (or full-time students under 24), the first ~$1,350 of unearned income (interest, dividends, capital gains) is tax-free
• The next ~$1,350 is taxed at the child's rate (usually 10%)
• Unearned income above ~$2,700 is taxed at the parent's marginal rate — this is the "kiddie tax"

For most families with modest custodial accounts, the kiddie tax is not a major concern. A $30,000 account growing at 7% generates about $2,100 in gains per year — right at the threshold. For larger accounts, consider the comparison table below.

What happens when the child turns 18 (or 21)?

At the state-specified age of majority, the custodian's control ends and the account belongs to the child outright. There is no mechanism to take it back, restrict how they use it, or delay the transfer. This is the core tradeoff of a UTMA/UGMA account: flexibility in what the money can be used for, at the cost of parental control at 18.

If you're concerned about an 18-year-old receiving a large sum unconditionally, this is a reason to also consider a 529 (restricted to education) or to have ongoing conversations with your child about the money as they approach adulthood — so the transfer is expected and discussed, not a surprise.

Comparison: which account for which goal?

Many families use a combination: a UTMA for general investing (birthday money, grandparent gifts), a 529 for college savings, and a custodial Roth IRA once the child has earned income. See The Custodial Roth IRA for why the Roth option is so powerful for working teenagers, and 529 Plans Explained for the education savings angle.