Since the 1970's investors have seen a massively rising tide effect of transition from exceptionally high interest rates down to exceptionally low interest rates as of present. That has served the golden generation well. Barring another rapid collapse and rise of interest rates, massive decline in prices, that history is unlikely to repeat.
Longer term (century+) stocks have managed to provide a 9% gross total return (assuming dividends reinvested) relative to 3.8% annualised inflation over the same period is suggestive of a 5.2% real benefit.
BUT! CPI inflation has been aided by technology/robotics. Fields full of farm workers replaced by machines operated by a couple of workers ... etc. i.e. production costs have relatively declined which has enabled consumer prices to relatively lag. Compare for instance that 3.8% to the average of house price, CPI and share price increases that annualised at 5%!
Taxation in the past was less forgiving as well. Around half of 9% stock gross total return arose out of reinvesting dividends. Historically a basic rate taxpayer paid 37% tax on dividends (1.7%).
Costs historically were much higher. Often >1%, and market makers had a field day with postal trading orders where they could widen the spreads out to 10% or more. £100/trade type broker fees were also much more common.
The financial sector is the worlds largest/richest sector. Within that private investors often have a tendency to lag the market due to buying high (greed), selling low (fear). Broadly its estimated that adds a 1.5% annualised drag upon portfolios.
Tally the reality and many investors might have been better served by simply investing in cash deposit accounts. Many pre-1970's mature investors were more content to hold safe savings accounts or bonds than 'speculate' in stocks.
My advice to the adult-kids would be not to be taken in by the financial sectors sales pitch. Often the suggested higher rewards from stocks compared to alternative assets are mathematically evident, but in practice only serve others not the investors benefit. It's more important to minimise costs, minimise taxation and invest in a buying groceries like manner (buy more when prices are low, buy less when prices are high). And diversify widely (which doesn't mean just a bunch of different stocks, but rather different assets with differing geopolitical risks). For instance high yield stocks are a invitation to be subject to ongoing/regular (dividend) taxation, such regular taxation risk can be reduced by minimising dividends. If net real gains are barely 0% then blending with other 0% assets that move distinctly differently to one another along with rebalancing will yield a >0% benefit (volatility capture is part of total gains along with income and price appreciation).
Don't get suckered in and believe that the next generation will get anywhere near the pension benefits, care benefits and/or investment reward benefits enjoyed by the previous generation.