Finlay - Basic photos

All,

These are some very basic photos, but I am looking for some suggestions on how to improve image quality.

I was visiting my sister and taking some photos of my nephew, Finlay. These photos were taken with low natural light. Using my 100 f/2.8 and ISO 1600 for the first and 3200 for the other two, I found it hard to get a nice sharp image. I used to have a 50 f/1.4 and really enjoyed it. I think I need to be looking for another 50 f/1.4. Is there anything else I could have done to improve the quality?

IMAGE LINK: http://www.flickr.com …s/gunnerphoto/8​285870868/

IMAGE LINK: http://www.flickr.com …s/gunnerphoto/8​284811775/

IMAGE LINK: http://www.flickr.com …s/gunnerphoto/8​285872728/