Think like a father-in-law, arranging marriage settlements for your child.

Lawyers would be involved, and in my experience lawyers spend a lot of time thinking about possible outcomes. One outcome of a marriage is that your child dies after having one or more children, leaving the spouse (not a relative of the father-in-law) widowed.

As a grandfather you want your money to benefit your own flesh-and-blood, not some random stranger (otherwise you'd just give your money to charity in the first place). If the money you are settling on your child goes to their spouse on the event of their death, the spouse may well remarry, have more children, and disinherit their first children in favour of the later marriage.

So, you make sure the marriage settlement is such that in the event of your child's death, their widowed spouse cannot decide to leave their money to anyone but your own grandchildren. A life interest provides for the widowed spouse, with the capital to go to your grandchildren.

I understand such arrangements are often done now in wills too.