In photoshop you can set the dimensions with the crop tool by typing them into the boxes at the top toolbar once you've selected the crop tool.
Example: if you type 6x4 and just drag the crop guide over the Mum's nose it would crop and then enlarge the image to 6x4. Conversely, if you drag the guide over the scene as you would like it cropped it would trim the bits you don't want and resize to 6x4 but the dimensions of the crop guide will stay in proportion so you don't get a messed up aspect ratio.
EDIT: I should really have critqued too.
I prefer the black and white but might have liked the midtones brightening just a touch.