Of course it depends where within Disney World that you're starting from but let's say that you begin at Downtown Disney - in that case the Florida Mall is about 12 miles away. I'd suggest taking I-4 east to exit 72, SR 528. Continue on 528 to exit 4, Consulate Drive. Follow Consulate Drive to Orange Blossom Trail and turn left onto OBT. It's about a mile to the Florida Mall which will be on the right. If you take the Sun Life Path entrance to the mall you'll enter the property at the southwest corner of the mall, the M&M Store is located at roughly the southeast corner of the mall buildings. I think that there's an outside entrance to M&M right next to a regular mall entrance.
It would probably take no more than 20 minutes from Downtown Disney to the Florida Mall by taking that route.
Dick Taylor