Imply a Narrative
Creating foreground/background relationships not only adds visual depth, but emotional depth as well. These adjustments suggest a more nuanced story than what we're getting from the stock photo.
The Power of Masking
From a holistic perspective, I felt the girl in the original photo had a potentially disruptive energy, as if the photo made her the focus instead of the family unit. I merged the two girls' faces to get an overall softer, more unifying effect.
The Sins of Stock
One of the greatest issues I've seen with designers is that they often use stock as they find it, they don't capitalize on the potential that's often right there in front of them.