Gay marriage activists have taken to claiming that redefining marriage will help children. Ryan Anderson responds that the opposite is true:

Marriage is society's best way of ensuring the well-being of children. State recognition of marriage protects children, we saw yesterday, by encouraging men and women to commit permanently and exclusively to each other and take responsibility for their children.

Laws on marriage work by promoting a true vision of the institution, making sense of marital norms as a coherent whole. Law affects culture. Culture affects beliefs. Beliefs affect actions. The law teaches, and it shapes the public understanding of what marriage is and what it demands of spouses.

But redefining marriage further distances marriage from the needs of children and denies the importance of mothers and fathers. Redefining marriage rejects as a matter of policy the ideal that children need a mother and a father. (Heritage)