Parents and children usually find it awkward to discuss money, especially when it comes to talking about the overlap of wealth and death. That's why 68 percent of millennials expect an inheritance, yet only 40 percent of parents will probably leave them one. But, it turns out, wealthy families may be even more uncomfortable talking about money than other families.

Only 10 percent of rich parents, the Washington Post reports, give their children a full picture of what they stand to inherit.

The reasons for their silence vary, according to the Post. Twenty percent of parents say they haven't started the conversation because they haven't made up their minds how much to pass on. Fourteen percent are waiting for their children to get older and, presumably, more mature. Ten percent don't want their children to anticipate wealth they may not receive. And five percent say, "It's none of their business."

American families do have a habit of burning through massive amounts of cash: 70 percent lose their wealth by the second generation, Time magazine finds, and 90 percent, or virtually all of them, have squandered it by the third generation. Although some have built, and sustained, successful, enduring dynasties — the Hearsts and the Rockefellers, for example, and, more recently, the Dursts — it is far more common for even the foremost families in the nation to watch their standing slip away.

The five Rockefeller brothers. From left to right: David Winthrop, John D Rockefeller III, Nelson and Laurance.

That's what happened to 19th century robber baron Jay Gould, who was once one of the richest men of all time. Thanks to mismanagement of his assets by his oldest son, and then by his grandchildren, his billions had dissipated within decades.

Could that be averted with some better communication between generations? It's unclear. But Forbes, delving into the history of the Hearst fortune, points out that sometimes a family business keeps succeeding, and paying dividends, because it is kept outside the family.

That was the secret for patriarch William Randolph Hearst, anyway: When he died, he made clear that he had no intention of allowing any of his five sons to take over his media empire. Instead, "control was to be in the hands of professional managers answering to a self-perpetuating board of trustees on which Hearst family members would have only five of 13 votes. The trusts would last until all the then-living grandchildren had died — an event likely to occur sometime around 2035. Any heir who challenged the will would be disinherited."

Regardless of whether his plan to privatize made his heirs happy, it ensured that they would remain rich.

Today's rich parents would do well to at least make a plan, experts agree. As Bill LaFond, president of family wealth at Wilmington Trust, tells the Post, "Everyone needs to be ready. You, the wealth holder, need to be ready for that conversation, and you have to be comfortable that your kids are ready for that conversation."

Don't miss: Self-made millionaire Eugene Lang set his kids up for success by not leaving them a dime

Like this story? Like us on Facebook!