I assume you mean Med/Peds, referring to "Internal Medicine/Pediatrics". A person who chooses to do a residency in Med/Peds rotates through work in both. Generally, once in practice, they can either work in a hospital or clinic, and see both adults and children.
In many schools, Med/Peds is much more popular than Family Practice. Med/Peds residency lasts 4 years, while Family Practice takes 3.