Well, you are supposed to go to a professional piercing studio to get help gauging your ears, and in most places you have to be 16 or 18 to even step foot in those shops.
To gauge anyone under legal age of piercing would be considered mutilation and child abuse. Those are pretty hefty charges that anyone with half a brain would want to avoid. Even if the parent isn't the one who did it, the authorities would come looking at the parent as the primary custodian and ultimately responsible for their child.
On a side note, I disagree with being able to pierce your baby's ears. That in itself is mutilation and child abuse, in my opinion. There should be no "fine line" in this matter.