I think that is something that has to be shown or not shown based on an intimate understanding of an individual child in order to accurately predict their reactions and the ability to follow up if some are left bewildered, scared, or unduly worried about the risk of people they love dying next time the family goes for a paddle.
That might be a bit hard to achieve with a whole classful.
My son saw his grandfather laid out right before the funeral. He was Okish about it. On the other hand he utterly freaked out recently at the not very close sight of a (non mangled) dead kitten at the side of the road. I dealt with both in a manner that was adapted to a little boy I know really, really well, with a full time availability day and night (especially at night where dead kittens are concerned). I think in part what coloured the difference in his reactions was the level of preparation he had, he know his grandfather had died, he know he could come and see him to say goodbye. Whereas the kitten came from nowhere and his previously happy state left his wide open for shock and being very, very upset. I'm kind of leaning towards images of death in a classroom having too much potential to fall into the catagory of the latter.
They are only five, I'm not sure what the rush is (certainly in an educational context) to show them that our hold on life is not secure, within our control, or something we can count on.
I'd guess that for the majority the concepts involved would go right over their heads, so what did showing the images hope to achieve ? For a minority, be it due to insecurities, recent losses in their family, being a bit afraid of the sea already, it could have risked setting of some upset.
Out of sheer curiosity I'd love to know what the original teaching point was that led to the choice in the first place.