Instead of desaturating, or even using Photoshop's "Black and White" dialogue, I used a proprietary plug-in: Nik Silver FX Pro. I also used Nik's Dfine 2 just on the sky in order to minimise the noisy "jaggies" I found there, obviously the result of the required compression needed for uploading to TE.
Hope you don't mind: I just thought an alternative take on your beautiful shot might be valid.
First I had to select out the white frame, as that would have given me 255 highlights. Then levels highlight picker was pointed at the foam on the waves. This both lightened the overall tones and changed the colour balance in favour of warmer reds/yellows (probably more like the colours of the original scene). Then a new selection just of the dark areas of the children's faces and clothes. Again a mid-tone lightening using Levels of that selected area allows us to see their features more clearly. What do you think?