To be fair, it's three kids, not one kid. Which it literally says in that article.
So it would technically be $21k per kid. And may be subject to change once they start hitting adulthood (one of them is going to be 18 in about 2 years). Though from that article the bulk of the money is going to the fact that she's unwilling to move them out of the rich neighborhood they've been growing up in, so it's a "living in the style to which they are accustomed" argument, where she doesn't want to start living closer to her actual means.
But the US court system has been horrifically biased against men in divorce, custody, alimony, and child support cases for a looong time now. And it tends to be even worse in California. So if anything he's lucky he managed to argue it down to $63k, when she was apparently asking for almost three times that.