I met a girl in college who claimed she first sex at the age of 10 with an 8 year old boy. And honestly, there are no laws on the books (that I am aware of) prohibiting children from having sex with each other. The only laws I know of prohibits adults from having sex with kids.
I also think LuckyTom has some very good points. If one of the parents took her to the doctor for an abortion at age 11, and told the doctor she got pregnant by a boyfriend, how could he know there was child abuse to report? How does anyone know if the Doctor knew who really got her pregnant? Did the girl tell him?
If the doctor did not know the father got the girl pregnant, the doctor would then not have seen it as a child abuse matter, but a family matter, and not reporting it was to protect the privacy of the family and the girl.
However, it is the perfect case for the anti-abortionists to go after as they wish to attack abortionists (the Doctor) and the patient-doctor privilege, the privacy of which is one of the main underpinnings of Roe v. Wade.
On the downside for all: if privacy between doctor and patient is determined to be null and void, all parents may expect to be investigated, and possibly loose custody of their children, whenever a child in their care becomes pregnant.