So let me get this straight. If everybody does it it must be legal?
No.
If you kidnap a baby and raise it as your own, the kid's immunization records shows you as the parent, the kindergarden school papers show you as the parent, Kinko the Klown has records of being the clown at her 3rd birthday party, and your neighbors all say you had the kid when you moved into the white house, then as far as this court is concerned, you are the parent.
No birth certificate required.