Thank for the kind words Patti. I have indeed flipped over to this thread and added more than a line or two! You're very right about capturing in colour - the sepia doesn't work as well.
Let me take each component of your portraits individually. First up is the lighting which you've handled well. It appears as though these were taken on a cloudy day or with the aid of trees as cover, particularly in #2.
However the way you've used the tree cover provided a problem - there's a light green cast. This could be remedied with a little post-processing or at the time of taking the photo. One option would be to use a white reflector to push light back on the face of your daughter. Outdoor portraiture seems to be popular around this time of year, and so I've covered this in a recent blog entry
Lighting aside, the composition's been rightly commented upon and "just take the pix" has given out some good basic pointers regarding this. However the rule of thirds is only a basic construction and doesn't have to be followed religiously. Let me dissect image #1 and the composition.
Here's your original:
It's well exposed and the lighting isn't half bad. The central composition is very elementary, but isn't the largest problem. This is the lack of background interest to the right of the frame in balance to the left. In ideal circumstances, you'd make one step more to the right and take the photo with less of the green leaves in the background and with your son slightly off-centre. However we can't do this perspective change in post-processing, but what we can do is crop. Let's have a look at "just take the pix's" suggestion:
Edit by "just take the pix":
Composition is arguably stronger than your original because of where your son is placed in relation to the frame. There's also the elimination of all that area of disinterest to the right background. Why you don't like this version as much is probably down to this cropping off of the green leaves. Now the background has been made to appear lighter because it's mainly dominated by the left of the frame; this means you've now got much less contrast between your son and the background. What I also don't like is the cropping off of his legs which I thought to be a cute characteristic. Which brings me to this:
Let's go through this version. I've cropped off a little from the right but not to the same extent as "just take the pix" but crucially I've kept the legs. The cropping removes some of the disinterest and pushes your son away from frame centre. I then layer masked and used unsharp masks and subtle changes in curves and levels to adjust how the lighting appears. The aim in this manipulation was to pull more contrast out between your son and the background and to make the lighting more soft. Finally I added a little saturation boost and the temperature warmed by 400K to boost skin tones.
There's a side-by-side comparison with your original below. Let me know what you think of this version.
I'm now going to make a full circle and return to what Patti picked up. Let's be kind and just say the sepia version doesn't work in this instance. The reason for this can be similarly explained like before - you've removed practically all the contrast between your son and the background so he barely stands out. Sepia might have worked if you had a vastly shallower DoF. I can't go by without a word on the composition as well - the placement of your son in the frame is good, but there's no interest in the background and so a smaller depth of field could have given more distinction between subject and background. There's also too much space at the bottom of the frame compared to the top.
Hopefully this has been worth my while. Do post questions/feedback to things I may have not made clear or omitted and I'll try to get back to you.
They're alright for a first attempt. Thanks for sharing and I'll leave you with your original and my edit for a side by side comparison.
EDIT: corrected typo.