The Star-Tribune hit the nail right on the head in their editorial about "kids.us." The question to ask is: who will use this? Who will it benefit? Certainly anybody doing Internet filtering today is not going to add "*.kids.us" to their whitelist. (Although if somebody announces such a plan I'd be interested in hearing about it.)
I'm annoyed that from a government perspective, 12-year-olds and 7-year-olds are equivalent in what they should be allowed to see.
I'm also worried that the failure of ".kids.us" would increase the pressure for a worse "solution", like a ".xxx" or ".prn" domain. Not that they would work, either.