Not sure if you considered inflation

Common knowledge of average return for S&P 500 is around 10%. However, if adding inflation, this number drops to around 7%. But this number may not be accurate also because inflation is calculated based on CPI. It may not reflect the true inflation.

However, stock market is one powerful wealth building tool for average joes. You need to start as early as possible. If you start to do that for your new born, even just put in $1000 per year. As age of 65, he probably would have around $6 million + (by the way, this is just a theory. if you choose the wrong account for new born, it can have a significant impact when college time comes).