U.S. savings bonds
How to Save for College: I Bonds and 529 Plans Help Reduce Student Loans

The golden age of I bonds may be coming to a close, but they still offer some perks. One often-overlooked use case: Saving for your kid’s future college tuition.
When used for higher education, the interest accrued on Series I savings bonds isn’t taxed by the federal government as long as the owner meets certain criteria, including an income cap.