Some fairly decent shots there mate given the conditions. It's pretty tough shooting indoors when you want to be in an area completely lit up and only one window to a side.
composition is important, rule of thirds etc etc...
I think there's a few of the shots where you'd have done better with the kids facing the window. the highlights are pretty blown out in places, which I find happens quite easily with Digital if you've got to over-expose a background to expose the subject.
try shooting outdoors or something, it can be awkward shooting with furniture etc knocking around indoors and getting in the shots, which has also lead to you using a wider end of the lens and a bit of distortion.
I'm sure some people would mention having a shallow depth of field when shooting people, but I feel a lot of people use it either because they've spent £1k on a lens so need to justify it, or they're not creative enough to use the background to their advantage. Ryan's one of the only photographers I personally know who actually uses it to his advantage.
best ways to improve? In my opinion, shooting all the time, and looking at
good photos are both key. if you look at a high standard of work, you're more likley to gain inspiration / ideas etc from it.
Taking critisism rather than compliments is also a good way to improve. I see a lot of people getting compliments like "hey, nice shot!" and they think that makes them a good photographer. I'd rather have someone tell me what they don't like about my work, that way you get an idea of what you can improve rather than being happy with average images.
Oh, and shooting manual a good way to learn the camera, but don't feel you have to do it because photography geeks say it's 'better'. AV / TV / P mode are equally adequate if you know how to use them for your needs.