I've got a tip for you suecate
I've launched over 2000 students on the first dive of their life and seen a few anxious faces on the surface before the dive starts.
I've learned to tell them to 'look under the boat', I say it with some excitement like there is something under the boat I want them to see. This gets the face under and looking around and avoids that slow sinking as the water line rises feeling that reminds them of an Alfred Hitchcox movie. :-)