Here's what I did:
1. Made a copy of the basic layer, added channel mixer to it and adjusted the values as follows:
<Green> red 10 | green 60 | blue 50
<Red> red 90 | green 0 | blue 20
<Blue> red 10 | green 40 | blue 90
2. Made another copy of the basic layer. Applied channel mixer to it with the following values:
red 55 | green -5 | blue 50
Selected the child with the lasso tool, added 2px feather to the selection, inverted it and hit delete. This way the color layer shows from below and the kid's face and legs are the only thing that needs to be colorized.
3. Added new layer, blending mode set to Color and put some color on the child's face. Made a marquee selection of the lower part of the image (it has some red nuance left) including the chair, excluded the red dress from the selection, then desaturated the reds.
That's it!
Hope it's helpful