Reminds me of my girls when they were young. They made a play house out of boxes our furniture came in the middle of our den. I love the kids expressions.
The expressions on the kids' faces are priceless, but the eye has to hunt for them when you first look at the shot because the majority of the image is taken up with the less-interesting details of the box surface and the wall/door/floor. I can see how this can be taken as the children playing a "hiding" game, but, for me, the faces of the children should be more prominent.
Maybe a shot directly down into the box, or a different angle altogether (such as the kids peering over the edge of the box) would have made this more interesting.
I like the color conversion a lot - although some, who prefer less contrasting black and white images, would prefer less contrast so that the girl's head does not appear to be floating by itself.