I agree with picking your battles. Eight seems a bit young but it's not worth denying since it's also not a sin. There should be some restrictions on what type of earrings. I certainly wouldn't have wanted my girls to have long dangly earrings at that age when they were out playing, climbing trees, etc.
Considering how cruel some kids can be when somebody doesn't have what they have, if my child was going to have to face taunting over something like not having pierced ears, I would see that as way more of a problem than the piercing itself.