These suggestions are good, but not just for “greening” the party. They also help encourage creative thinking, on the parents’ as well as the children’s parts! I especially like the suggestion about having an experiential birthday party for your kid. Don’t you recall the parties you had when you went horseback riding, jumped on a trampolene, or visited the carosel?
At the end of the day, though, I don’t think the party needs to be “greened” so much as just simplified. Explaining to your kid that he can’t have plastic kazoos because they kill dolphins might be a major downer in the end. You could just have a party and have it be the way you do things, just because. Making a lifestyle change may indeed take some explaining to kids, but ultimately it’s just another way to live by example for you as the parent.