Get him as close to the light source (window) as possible and use a reflector (white poster board is all it takes). In addition to the white balance, I would check the shutter speed. It seems pretty fast causing the photos to be underexposed. It is possible to take great portraits with natural light. A little post work will fix these that you've shown here just fine.
Here's a photo I took with minimal space between me and baby and as close as I could get him to the window for light. I did a little brightening up in post. This was my first attempt at baby portraits and I used the 50 mm f/1.8 lens.
Camera: Canon EOS Digital Rebel XTi
Exposure: 0.013 sec (1/80)
Aperture: f/2.8
Focal Length: 50 mm
Exposure: 0.00
ISO Speed: 200
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