from my research, my opinion is
1) for a will, all children should be named. then if the will is gonna distribute any assets, it specifically names those people who are receiving stuff.
2) for a trust, you specifically name your beneficiaries, and how you want to distribute the trust assets to them. you then very simply exclude everyone else with a phrase like "no one has been forgotten. anyone not mentioned as a beneficiary is not a beneficiary."
and if you want to be especially careful, you can say something like "and this includes my son john, who receives nothing."