Well in the sequels it was very detailed especially in the scene the OP is talking about in this movie. There's also the beach scene in the second movie. Malcolm has on a fake arms and legs covered with a realistic skin covering to add to the weight of Big Momma that really looks real. It seems like he only goes heavy with the suit details when it's for scenes like the beach and the art class where he has to show some skin and he obviously can't be wearing a flat-out fake torso suit. His cover would completely be blown if he was just walking around in the fake looking torso suit and his regular body size arms and legs popping out of it.