For parents and grandparents thinking about their children’s future, a Children’s ISA account remains one of the simplest and most tax-efficient ways to save for a child. Yet one key choice shapes how much that nest egg can grow: should you opt for a Cash ISA or an Investment ISA?

Understanding how each works and what implications inflation can have, especially on cash, can help you make a more informed, long-term decision.

The Two Types of ISA for Children

A Children’s ISA (also called a Junior ISA) lets families save or invest up to £9,000 per child in 2025/26, entirely tax-free. The money belongs to the child and can’t be touched until their 18th birthday, when the account converts into an adult ISA.

There are two main options:

• Cash Junior ISA: Works very much like a traditional savings account. The money earns a fixed or variable interest rate, with no exposure to the stock market.
  
• Shares Junior ISA: Invests in funds or portfolios of companies and bonds, meaning values can rise or fall, but with greater long-term growth potential (and risk).
  

Parents can split the £9,000 allowance between both types if they wish.

Cash ISAs – Steady but Slow

A Cash Junior ISA offers certainty. Balances don’t fall, and the returns are easy to track. In recent years, interest rates for children’s cash ISAs have hovered between 3–5%, depending on the provider.

That seems attractive, until inflation is factored in. If inflation averages 3% a year, a 4% interest rate delivers only a 1% real return. Over 15 years, that small margin adds up. A £9,000 annual contribution could grow to around £170,000 in nominal terms, but only about £145,000 in today’s money after inflation.

For families prioritising safety over growth, cash still has a place. It suits those with shorter time horizons or who want the reassurance of guaranteed returns.

Investment ISAs: Harnessing Growth

A Junior Stocks and Shares ISA, by contrast, invests the allowance into markets. Over the long term, global equities have historically returned 5–7% a year after inflation — though with short-term ups and downs.

Using a conservative 5% real annual return, which is the average from the Children’s ISA based on historical figures, that same £9,000 invested each year could be worth around £210,000 after 18 years, roughly £65,000 more than the cash example above. The difference is the power of compounding: each year’s gains begin generating their own returns, magnifying growth over time.

The trade-off is volatility. Markets don’t move in straight lines. But because Junior ISAs lock funds away until adulthood, they allow time for downturns to recover. 

Understanding the Inflation Effect

Inflation quietly shapes every savings decision. A £1 toy today may cost £1.50 by the time a child reaches 18. Cash accounts that don’t outpace inflation effectively lose value in real terms. Inflation is often known as a sneaky thief.

Investment ISAs, while riskier in the short run, have a stronger record of beating inflation over long periods. This is why advisers often recommend a mix tilted toward investments when the savings window is a decade or more. This could be an important consideration for parents looking to invest now, as, at the time of writing, inflation in the UK seems sticky in the short to medium term. 

Making an Informed Choice

When choosing the best ISA for kids, it helps to start with time horizon and comfort with risk:

• Under five years: A cash account provides certainty and accessibility.
  
• Five to ten years: A blended approach spreads risk.
  
• Ten years or more: An investment ISA has greater potential to grow and preserve value against inflation.
  

Whichever path you choose, maximising the 2025/26 allowance of £9,000 ensures no tax-free growth opportunity is wasted. Regular contributions, even modest ones, build momentum, and starting early amplifies results.

A Partner in Long-Term Growth

At the Children’s ISA, our role is to help families understand how these accounts work and why a long-term, investment-focused mindset can make such a difference. With clear guidance and transparent performance data, parents can make decisions that give their children a stronger financial start.

Saving for a child’s future isn’t about chasing quick wins. It’s about putting time and compounding to work,  building a foundation that grows alongside them.