What do doctors do in a physical for 12 year old girls?

They check breathing, heart rate, eyes, throat, ears, etc.

They weigh you and see how tall you are.

They feel the testicles and penis (for a second).

Another answer:

Boys generally worry about physicals and doctors (especially females) messing with their "privates". At that age (11 or 12) pediatricians (kid doctors) rarely have kids undress. When kids are in their later teens, they will be asked to lower their pants, the doctor will feel for a hernia by asking the teen to turn their head and cough while the doctor feels above the testicles, nextto the penis. There is no medical reason to "feel" the penis, even for a second. If the doctor "feels" your penis for 2 seconds or more he or she is "fondling" you and I would report it to my parents and refuse to return to that doctor.