The b&w image using the default settings. I find it to be a bit washed out and 'blahh'
To make the child stand out from her father I lightened the red using the white balance tool, Or more accurately the white 'non balance' tool. I moved the temperature. tint and r&b equalizer up until I had a red dress tonality much lighter than her father's shirt. Unfortunately the histogram is now too far to the right
To fix that problem I used a 'before' parameter curve.
This curve gave a full range of tones. The kid stands out. The background is busy but not obtrusive. The details on the screen of the tablet are still visible. I should also mention that with the new 4.2.1 build there is much more difference between curve type than with earlier versions. Using the same curve settings, the 'b&w film like' selection had much lighter darks that the 'b&w saturation and value' selection .
As for using an 'after' curve, my take is that all the real action is in the 'before' adjustments both inside and outside the b&w tool. If you want to do something like color toning with the LAB tools, go at it. But once the tonality and conversion parameters are set any 'after' curves should work the same way similar curves work outside. the b&w tool. So I will leave that for another discussion
The final image. Enjoy the kid's hands and frown. My balloon caption is "STOP, SNEAKY PAPARAZZI !!! MOMMY is taking MY PICTURE!!"
And for the record here is the totally non white balanced color image that produced the final b&w.