I actually like the first picture better as the off-center composition and the darker background helps me focus on your son. In the second example, the camera is too bright and I focus on that. Also, he is just enough off center to make me feel uncomfortable about it, but not far enough to really create a tension (google "rule of thirds"). What you have done well in the first and fourth pictures is to get at his level to see the world from his view. The other two have a "parental", down-looking view which I think is not as good. In terms of what white balance to use, in the third example, you probably needed a tungsten WB, or AWB. As you are shooting raw (you mentioned in your first post), you can correct this in Post. In general, what will be best for a photo is to avoid mixed light sources (like daylight and tungsten or fluorescent and tungsten, etc.).

In terms of your original question about whether you are getting better, try submitting your very best shot from when you first started and then your very best from recently.