Use Shoebuy, sign up to become a member to get the 10% off, and find a good code for their website. We've bought several pairs from them and they always have the best price.
The only problem we've had is that they list every style and color on their website, but when you go to order them, sometimes they don't have the right size for you in the style/color you want.
One last thing, please PLEASE don't believe anyone who says that the knockoff brands are just as good as Crocs. They look similar, but that's about as far as the resemblance goes. They don't provide ANY of the benefits of Crocs, such as the patented CrosLite material, proper fit, anti-microbial aspects, etc. Knockoffs are made with the same cheap material that every other cheap kids shoe and sandal is made out of. They're just made to resemble Crocs. If you were going to buy your kid cheap shoes anyway, then the knockoffs may be fine for you. But if you are expecting to get the benefits listed on the Crocs website, there better be a Crocs logo on the shoes you buy.