If we go by this distinction, default atheism then is also actually an entirely useless label, as far as labels go. So we might as well ignore it completely and stop using it.
Babies just don't do much. They don't embrace any world view. They don't have opinions about anything. It's not telling us anything when one says that babies "do not believe in a god nor possess any knowledge or opinion about one". Well, of course they don't!
I can see it's usage being relevant in the case of grown ups who have no knowledge of the concept of god (though i would still feel it's an unnecessary usage), but in babies it seems more like grasping at straws.
It is somewhat of a useless label except in respect to the claim of theism. If someoene is asked if they believe then "I don't know" and "no" both amount to not being theist. Knowledge of isn't necessary because belief doesn't require knowledge.