A lot depends on the family dynamic. For our little delegation, Mrs. Ambassador leads,with the Ambassador following as the sweeper. We use radios in the Parks, and carry cell phones. Mrs. Ambassador has not allowed GPS transponders as yet.
Some days we wear family t-shirts in the same color with similar designs. We put pre-printed labels with last name, resort and cell phone number in some inconspicuous space where they may not fall off before noon. We do take a digital photo at the start of each day. We also point out CM's and identify what they look like, with instructions to seek them out should anyone be temporarily separated. Which has happened twice in the MK, for a few anxious moments.