kid's diapers in US

You can get diapers anywhere and everywhere in U.S. The most common brands are Huggies and Pampers. Other brands like Luvs are also available. But I think Luvs is available only at Target.
Buying diapers at wholesale stores like Sams Club or Costco is cheaper. However you have to take membership at these stores inorder to make a purchase. These stores have their own store brand of diapers too.

You can also get diapers at walmart, target or any drug stores like CVS,rite aid, walgreens etc. You can also order online at www.diapers.com.

I personally use Huggies and I love them so far. And I buy them from Sams Club.