For our Christmas present my DW's father (who happens to be an OG mustachian) gave us all of her EE US Savings Bonds that he bought for her in the 80's. What I didn't realize is they continue to accrue interest beyond their face value. Since they were from the late 80's the interest rate on these bonds is 4%.
They are going into a VERY safe place until they're fully matured in a few years, as 4% risk-free interest is not something that is easy to run into these days!
We're definitely inspired to set aside a little 'stache for our kids.