My friend's grandparents gifted them (through their parents) several US treasury series EE savings bonds when they were born. I don't know the exact details, but many were purchased back in 90's and some in the 00's when you could still get the paper bond and the interest rates were around ~4% (on similar bonds they're now 2.7%). EE bonds are savings bonds and differ from other US treasury bonds in that there's no coupon (payouts) and the interest compounds. According to the treasury's website:
Series EE savings bonds are a low-risk way to save money. They earn interest regularly for 30 years (or until you cash them if you do that before 30 years).For EE bonds you buy now, we guarantee that the bond will double in value in 20 years, even if we have to add money at 20 years to make that happen.
A few of these bonds matured already (and had stopped paying interest awhile ago - yikes) and they were excited to see that the payout on some will be roughly double their face value (e.g. some of the $10k bonds are worth ~$20k). Some of the other bonds haven't matured and they are considering holding onto them to "make sure they double." I wasn't sure I should interject but I felt like I had to.
I described that (accctually) the real, inflation-adjusted value of those bonds had not doubled (they went up by ~40% afaict). Also, that using even the second most vanilla investment strategy of putting $10k in the S&P would have produced much higher yield (~10% CAGR starting in 1995 for 30 years would accrue to ~$170k afaict .. albeit with much higher risk).
It was exciting to experience the thrill of money turn into more money all on its own over a long period of time - even indirectly like this. I was almost excited enough to not think of the gains they lost by being so conservative.