Check out: HOW TO: Zoom from the Feet to the Head (Full Body)
Cut to the zone they are in, write:
NARR
Pause.
Then move the camera down to their legs and note the coordinates for the zoom. Copy them and put it into your script. Then move the camera up to their faces, note these coordinates, put it into your script and add seconds to the zoom so that it goes all the way up from their feet to their face.