A few thoughts, please take them as constructive help.
There's at least a dozen ways to do selective color in photoshop, google "photoshop selective color", or look at the FAQs here.
The picture could be better composed, and it looks out of focus or at least quite soft. To improve it try single centre point focus, and pay more attention to the background. Standing further away and using a longer lens gets less background in, plus blurs it out more. Also be careful if there's anything in your background try and be parallel to it so it's straight. Also when taking photos of children try getting down to their level, or lie on the ground.
Selective color's much overused. The face should be the focus of the picture, making it B&W is counterintuitive IMHO. If anything i'd use the channel mixer to make a B&W picture, perhaps 60% red channel, 20% each from green and blue, that's a starting point anyway.