AMCAS has an optional section that almost everyone completes where you list your parents names, indicate if they are alive (Y/N), their county of residence, highest education attained, last school attended, and profession.
One assumes when faced with an application from a physician's offspring, that you have an inside scoop on the demands that medicine makes on a physician's time and some of the struggles and the rewards. Saying specifically that you shadowed doesn't really add much. If you wanted to list the shadowing as one of the three most important experiences and mention that because your mom is in primary care, you chose to shadow specialists to get that perspective, that would be okay.