Some models does not like light
There are so many similar photos of babies out there and you just have to try not to fall into the trap to do the same. Of course you look at a picture and you think... I want to learn how to do the same and for sake do. But change it. Steal with pride and take inspiration but make it your own. If you are using flash, the trick is not to let the light hit the background and to use a Gary Fong or home made Honey comb grid to focus on the face and to seal of the light hitting the background. You can find many DIY project even using toilet roles. Another of my own invention is to take and umbrella and but news paper inside the umbrella to protect the ligth from going in the direction of the background.