Bryan Caplan looks at twin studies and concludes: Have More Kids. Pay Less Attention to Them (WSJ):
The obvious lesson to draw is that parents should lighten up. I call it “Serenity Parenting”: Parents need the serenity to accept the things they cannot change, the courage to change the things they can, and (thank you twin research) the wisdom to know the difference. Focus on enjoying your journey with your child, instead of trying to control his destination. Accept that your child’s future depends mostly on him, not your sacrifices. Realize that the point of discipline is to make your kid treat the people around him decently—not to mold him into a better adult.