Pity the poor millennials.

The 83 million or so members of this generation – a quarter of America’s population, the largest age cohort – have every facet of their lives studied by those who want to analyze their behavior, mostly in order to better sell them goods and services. The financial services industry is no different.

We know 72% of millennials plan to focus their spending on experiences rather than big-ticket tangible goods, such as new cars. Facebook has told us only 37% have a financial plan, although 86% save. More than half told Fannie Mae that debt is stopping them from buying a home. Another survey found that only 20% believe they’ll be able to retire at 65, possibly because 63% aren’t saving. (What, you wanted these analyses to be logical, coherent and consistent?)

Is there more to be learned about millennials and their attitudes to money? Fidelity Investments thought so, when it set out to interview 305 of them. What it has brought to the debate, in its just-released Millennial Money Study, is the nature of the relationship between members of this possibly overstudied demographic and their parents.

Struggling under more college debt than any generation to date, millennials graduated into a tougher job market than did baby boomers, Gen-Xers or others. The result? They are more likely to remain dependent on their parents long into their 20s.

John Sweeney, executive vice-president of retirement and investing at Fidelity Investments, was startled to find that since the firm last conducted its survey, in 2014, the proportion of those polled who are living at home has gone up 50%.

“Today, 21% of millennials live at home, up from 14% – the percentage of millennials receiving some form of help from their parents is also very surprising at almost half,” he said.

Indeed, the survey showed that a remarkable 67% agree that it’s acceptable for millennials to move back home with their parents, and twice as many millennials say they have done so than members of Gen X. Only 9% of baby boomers surveyed went back to live at home after college, but 25% of millennials have done so.

Help from family comes in the form of more routine items, too. Parents assist with 16% of purchases of clothing, help meet rent or mortgage payments 12% of the time, and assist with utility and/or cellphone bills for 14% and 21% of respondents. One in five reported their parents helped out by paying for groceries. Netflix bills? Yup, about 14% of respondents said parents will cover those, too.

No wonder millennials are doing better at saving today than they were two years ago. In 2016, 85% reported having some kind of savings, up from 77% in 2014, with 59% having set aside a remarkably high average of $9,100 in an emergency fund.

‘Only a small percentage identify as investors’

Fidelity’s study reveals three big problems – and they are big ones – with millennial attitudes to money. The first is one that Fidelity itself identifies.

“Almost half identify themselves as spenders; almost half as savers,” Sweeney said. “But only a small percentage identify themselves as being investors.”

Sure, saving is great. But to have any chance of building a retirement nest egg, millennials will have to break through whatever barrier is preventing them from becoming investors – whether it’s psychological or a feeling that they don’t know enough to get started. Keeping their cash in a savings account simply won’t be enough, at near-zero interest rates, to stay ahead of inflation over the next few years, much less the next few decades.

The dollars you invest in your 20s are worth exponentially more than those you invest in your 30s or later, thanks to the power of compound interest: the sooner your money starts generating interest or profits, then those interest payments can be reinvested and begin earning more for you, etc.

Make a $5,000 investment in a Roth IRA at 20 and if you earn an average rate of return of 8%, by the time you’re 65, even if you don’t invest another dime, it will be worth $180,000 – that’s compounding at work. Wait until you’re 40, make the same investment and at 65 you’ll have less than $40,000. Waiting 20 years to make a $5,000 investment would cost you $130,000.

It’s that kind of short-sightedness – the emphasis on saving rather than investing – that led to the results in last August’s poll from Wells Fargo, in which 64% of working millennials said they couldn’t see themselves ever becoming millionaires.

In fact, if they start investing now, and keep contributing to a systematic investment program, retirement assets of $1m is an entirely reasonable goal for someone who hasn’t yet turned 30 – even with college loans to repay. You stash the money in a tax-advantaged retirement account, take advantage of employer matches and allocate a portion of your raise every year to your retirement fund – and make sure to invest in something other than money markets or other low-return products.

True, it probably won’t work if you’re only earning $20,000 a year, or endure many or prolonged periods of unemployment. But it’s not impossible.

Fidelity emphasizes that millennials see their parents as strong role models, noting that two-thirds thought their parents offered a good example and had learned from past mistakes. On the other hand, there doesn’t seem to be much communication between the generations.

“They are learning from their peers and from social media,” Sweeney said.

Peers can give you tips on the best personal finance or budgeting apps, but when tough times come it will be useful to be able draw on the experience of those who have been through the fire. How do you budget after a layoff? How do you sell the house you just bought? In some life situations, it isn’t always peers’ experience that is most relevant.

There is another lesson here, for both millennials and their parents. It’s tough to negotiate the rules when an adult child moves back home and becomes financially dependent – even for small things – on his parents once again, especially if he is earning some kind of income.

That’s particularly true for this generation of parents, who may well have seen their own retirement savings eviscerated by the financial crisis and who are trying in the final years of their working lives to save every penny they can. Now, money that they might have earmarked for their retirement fund is going to fund their adult child’s mobile phone bill or groceries – which can add up to nearly $15,000 a year.

They might not begrudge it – they know their help is needed – but they must be aware of how that child’s situation is evolving.

“Parents should avoid letting their child’s lifestyle expand on their own budget,” Sweeney said. “Charge a nominal rent and do something with the money: subsidize your own retirement, or put it into a wedding fund or set it aside to finance the downpayment on the child’s house.”

There is nothing worse for a young adult than to move into her first apartment and come face to face with financial reality for the first time at 26 or 27, never having been fully responsible for paying all her own bills before until then. Who – parent or child – wants that to happen?

Inevitably, millennials will remain the research guinea pigs for Fidelity and countless other businesses, all eager to know how they think and how they consume.

Hopefully, as the surveys keep rolling off the presses, we’ll see millennials emerge from under the shadow of all that college debt and – crucially – learn from their elders not to delay too long in starting to shift from saving to investing. Because there just aren’t any do-overs.

•This article has been amended to correct a name