"The kids thought they were getting $50 million and then they find out they're only getting $5 million," Abati says. "If you don't tell your kids, and they had an expectation that then does not play out the way they thought it would, it can be very painful."

Some wealthy parents simply don't believe their children are mature enough to handle a large influx of cash. They think their children will squander it. Nearly half the U.S. Trust survey's respondents, for instance, believe their children will not reach a level of financial maturity until they are at least 35. Some fear their children won't ever reach it.

Action movie star Jackie Chan, at an awards ceremony for his son in Beijing, said he would not leave a cent to his son, singer Jaycee. Chan, who had already willed half his fortune to charity, was quoted by the Chinese media as saying, "If he is capable, he can make his own money. If he is not, then he will just be wasting my money."

Some parents feel their children are of an age and level of financial independence that they don't really need their parents' help, and so the parents pass their money on to their grandchildren, says Danielle Mayoras, an estate planning attorney in Troy, Mich. Mayoras says she had a client who structured his will so that the children wouldn't receive any money until they turned 65, and even then, it was just the income stream from the assets, not the principal. The principal was going to go to his grandchildren.

"In that case, the parents knew their children spent their money frivolously. It was like water in their hands," Mayoras says.

Emily Bouchard, a family, wealth and money coach with Wealth Legacy Group, based in San Rafael, Calif., says it can be a little unfair because many children in wealthy families are in a Catch-22 situation: The parent who built the wealth is likely to be a type-A personality, meaning they're probably controlling and unable to delegate. And those very traits can make it difficult for the children to learn how to handle money. The parents probably didn't have the time or the desire to teach the children about money, and they were likely so controlling with it, the children were never able to exercise their independence or prove how responsible they could be, Bouchard says. The result, particularly in families with first generation wealth, can be dysfunctional children who either embrace the wealth and try to live off their parents in perpetuity, or rebuff the wealth, sometimes because they fear people are using them for their money, Bouchard says. In the end, the parents in these families are usually so afraid the children will be hurt rather than helped by the money, they opt to give most if it away, she says.

"The parent feels like if they leave their wealth to their children, there's more potential for it to do damage and harm. So they try to avoid all that by giving the money to charity," Bouchard says.

And then there are those who are so determined to keep their money in the family that they will cut off their children, lest their son- or daughter-in-law gets the family fortune in a divorce settlement. Frank Brogan, an attorney with Greenberg Traurig in Fort Lauderdale, Fla., says it's not uncommon for parents to fear that if the money goes to the divorced spouse, it won't make its way down to their grandchildren. To avoid that, they structure their estate plan so that a chunk of their money bypasses their own children and goes directly to their grandchildren.

"When I first started practicing, the in-laws would get something in the estate plan. A parent would say, 'My child is married to so and so, and I want to leave them a little something.' But with more than half of all marriages ending in divorce, you just don't see people leaving money to the in-laws, nor do you see people having their in-laws even included in the estate plan," Brogan says.

These days, parents are also pushing more of the estate down to the grandchildren in the event that their own children make poor financial decisions and the family fortune is exposed to their creditors. The parents will structure a trust to, say, give their child the interest generated by an asset, but the child can't get at the principal. That would be left to the grandchildren. By denying their children access to the principal, the parent effectively shields the assets from the child's creditors.