Hi Russell,
Des has pretty much nailed it with his suggestions.
For the shadows, your light is definitely placed too far to the side. Pull it around closer to the camera - more front-on to the subjects. As has also been suggested, a second light or a reflector, to camera right, would also be useful.
I am a little bit concerned at the light fall-off that I'm seeing here. Compare the apparent brightness of the light as it falls on the baby's face (camera left) with that of the light on the father's face.I do feel that you have good density on the father, and on the kids camera right, which leads me to believe that the light is a bit too close to the baby, and thus she is being blown.
The light source also seems to be unmodified. Something like a softbox would help to provide some diffusion here.
Someone commented on the visibility of the chair leg. While I echo that observation, I also wonder at the bare feet of kids, and the mother. And on the very lh edge, there's a little white splodge.
Where possible, the distance between the subjects and the background should be increased. You want to direct your light onto your subjects, but in this instance, not on the background. There appears to be some sort of a stain on the background near the mother, and the background is loosely crumpled. Nothing too wrong with either of those issues, provided that they cannot be seen in the image. As they can, there is.
Now, to better illustrate this, compare the lh side of the background in this image, with the background on the rh side. The light falloff is significant, and on the rh side it's exactly what is called for.
Sharpness, baseline exposure and wb are all nailed, and I'm comfortable with your angle of view and the basic pose as well.
You've done very well. A few minor adjustments, and you'll be there.