My biggest concern is actually health-related - children's feet are still mostly made of cartilage and don't finish developing until their teens! As a result, permanent deformity can result from wearing heeled or otherwise unnatural shoes at an early age. Heck, deformity can result from habitually wearing bad shoes at ANY age, but that's another story. My sister wore heels starting at age 13 and permanently fused the last joint on the first three toes; I wore nothing but tennis shoes and my yoga teacher said "Wow, your feet are amazing!" (Which was a little weird, but hey, I'll take what I can get.) The bones are so soft when young that the child may not even feel pain when they are being damaged.
Chinese foot binding, anyone?
Foot binding - Wikipedia, the free encyclopedia