That's recent, just as of the last couple months. Historically the children's foundations have been a sideshow and he's given the bulk of his wealth away to the Gates Foundation. You can see that from the dollar amounts: this year's gift to the children's foundations was 1M BRK-B shares (the equivalent of about $500M) to each, while he's given away a total of $66B, over 120x as much.

Though unlikely the case here, family foundations should always be looked at as a likely source of corruption.

You cannot bribe me directly - that would be caught. However you can donate money to my family foundation and my kids (or spouse) will draw a large salary from it while doing almost nothing and they do some good for the world so it looks like a charity. Of course the kids/spouse will support me in various ways that all rich kids will.

Again, probably not what is happening here, but every time you hear of a family foundation you should ask who they are using it to corruption in some form. Even when it doesn't seem to be you should still look.