I had always heard that they used the reject carrots that don't make it for the regular bags as "baby" carrots. Just grind down the ugly shapes and sizes to make them babies. I've also seen "baby broccoli" in the stores, which was really a different plant that looks similar to broccoli and is used in Asian cooking (gai lan). It does resemble small broccoli plants.
I noticed my packet of Christmas carrots had two round ends and was suspicious...I've seen those broccoli plants!