One thing I'm surprised the US hasn't done - maybe the trust in Congress and thus in the US Federal Government is too low to make it worth attempting - is what the UK did by owning a consumer bank. As well as the Bank of England, the UK owns several other banks but one of them is a more or less ordinary retail bank except it has no lending business, National Savings & Investment or NS&I.
Money you save at NS&I is just money the British government doesn't have to borrow on commercial terms via issuing gilts. They pay interest on it, because that's what they'd have to do if they borrowed it on the international markets, and it doesn't need an insurance scheme or whatever since if that money can't be repaid then the country is bankrupt, which means the currency the savings are denominated in is now worthless anyway.
Americans can buy gilts, but there doesn't seem to be a way to just keep your kid's birthday money invested in the United States of America as a concept.
[[One of the cute products NS&I has which does seem like it'd appeal is the Premium Bond, the Premium Bond is an investment in which you give up a small fraction of the interest rational people would receive in exchange for more fun. Instead of interest you get proportional chance to win larger tax-free cash prizes. So instead of £51 interest maybe it's 0.25% chance to win £20 000. If you like scratch-offs but wish you hadn't thrown away all that money buying scratch-offs this feels appealing.]]