It is effectively the same. Unless the parent sets up parental controls (which they aren't going to do) there's nothing stopping the kid from opting in.
You're making unfounded conclusions about a hypothetical feature Apple hasn't implemented.
I can think of at least one way to make it difficult for a kid to opt-in (I'm sure there are others): require the opt-in to be done online and require re-authorizing the credit card associated with the iTunes account. If it's good enough to get an email account out of a COPPA jail, it's good enough here.
