In order to selectively blur just the falling pieces, turn off all layers except for the layer set containing the falling pieces, then choose Cmd(Ctrl)/Option/Shift/N to create a new layer, followed by Cmd(Ctrl)/Option/Shift/E to merge the visible layers. This keeps all layers intact in case you want to make other adjustments, and it gives you a merged layer to apply the motion blur. An added benefit is flexibility in changing the layer's opacity, and position in the layer stack. Select the falling pieces layer and use a motion blur (Filter>Blur>Motion Blur) with 40 pixels at 90 degrees, and reduce the layer's opacity to 25%. Then move the blur layer below the piece's layer set in the Layers palette so that the motion effect will not overpower the falling pieces.
Once that's completed, add a layer mask to the blur layer and selectively mask out the bottom of each piece's blur so that it better conveys the downward motion. See the before image to the right, compared with the final, full page version at the top of the page.
As a final step, extenuate the drama of the sky and child through the selective use of the diffuse glow filter (Filter>Distort>Diffuse Glow with a graininess: 0, glow amount: 6, clear amount: 20).
Mark Beckelman is an award winning photographer specializing in editorial and advertising photo illustration. In 2004, he collaborated as lead digital photographer for Katrin Eismann's 550-page book "Photoshop Masking & Compositing," (www.photoshopmasking.com) creating and producing numerous digital composites, concept illustrations, and photographic examples. To see more of Beckelman's work, visit his Web site at www.beckelman.com.