If you want to scare the you-know-what out of your grownup kids, casually let them know that you are talking with your lawyer about leaving your assets to your descendants in "generation-skipping trusts." The name implies that somebody is going to be skipped when it comes time to distribute your stuff after you are gone, but "somebody" may only be the IRS, along with your descendants' creditors and ex-spouses.
Of course, if you want to, you can snub your kids and leave everything to their kids, but that is not usually how a generation-skipping trust ("GST") works. More typically, the GST agreement will name your children as beneficiaries, but not include a requirement that everything be distributed to your children. For tax and asset protection purposes, it can make a great deal of sense to have your trust agreement give your successor trustee the discretion to make (or not make) distributions to your children and their descendants, and have the trust last as long as the law of your State (or the State in which the trust is created) will allow. As long as the trustee is not a beneficiary or close relative or employee of a beneficiary, your descendants' creditors and ex-spouses will generally not be able to get their hands on any trust assets.
If you like, you can split your estate into as many GSTs as you have children, and then give each of your children the power to remove and replace the trustee of his or her GST. That way, each child controls his/her trust during his/her lifetime. You can also give each child the power (called a "power of appointment") to say where any remaining trust assets go after the child's death. The default in the trust agreement might be that the assets continue in a trust or several trusts for the child's children, but the power of appointment could give each child the power to change the percentages going to the grandkids and even add stipulations to how and under what circumstances distributions will be made to the grandkids.
If you do all of the above in the right way, you can be pretty sure that the IRS will not get its estate tax hooks into your assets for a very long time after you are gone. As long as the trust produces income, there will probably be income tax to pay, but payment of estate tax can be entirely avoided.
One of the best estate planning rules is that you can, within certain limits, write your own rules when it comes to your estate plan. Talk with your trusted advisors about the kind of rule book that will best carry out your wishes for your estate.