Maybe not quite a million miler; I believe that there is a cap of $30k per year (face amount) per person for U.S. Savings bonds.

As to bonds diversifying a portfolio, yes this is true. Strictly speaking bonds in that context refer to debt instruments, presumably via a mutual fund. But, 'tis true that these are debt instruments of Los Estados Unidos, hence they would round out a portfolio, too.

Personally speaking, I only purchase a few bonds here and there for the kids. Equities just make too much sense over the long haul. But, the kids get to see and hold the U.S. Savings bonds and this makes the money more tangible to them.