Baby carrots are the same species as regular garden variety carrots, they are simply harvested sooner, usually when they grow to a fingers length. In some health circles, baby carrots are thought to contain a richer vitamin and mineral content, however they are mostly eaten at this maturity level simply because they taste better, and are much more juicy and tender. In some cases, harvesting these baby carrots is done to thin out existing commercial carrot crops, and allow more room for larger carrots to grow.
There are a number of commercial growers within in the United States that specialize in producing baby carrots only, and these are naturally bred with this practice in mind. One of these cultivars is called Amsterdam Forcing. It's important to remember that some produce sold as baby carrots are not first level maturity carrots, they are simply full size carrots that have been cut down in size do to warping, cracking, or other forms of carrot distortion. The largest United State producer of baby carrots in 2006 was Bakersfield California, which made up one third of the total amount of baby carrots sold in the entire country. The two largest and most well known worldwide baby carrot producers are Bolthouse Farms and Grimmway Farms. Many of their baby carrot are sold throughout the world.