Ok, I'll offer a critique--please know I'm not trying to tear you down, just pointing out a few things that I've learned in my short time as a photog.
This is a tough shoot just in the way you have it set up. I'm guessing you're using the on camera flash--which tends to be really tough to control. Often you get really harsh shadows etc.
1. The plush toy is way blown out--looks like his fur is not only white, but a tad reflective as well. Kind of a double whammy. Composition--the crop is interesting, but it feels a bit tight to me? He looks like he's sitting pretty far behind her. The posing kind of accentuates their body types. He's skinny as a rail, and she's a bit more voluptuous, so maybe put him in front, with her behind with her arms around his neck on his chest--this might help even things out for them.
2. The one kid looking off in another direction is distracting, as is the bib on the other. Maybe pull back a tad to show either more of their feet and mantle above. Her white wrap is overiding all the other tones in the portrait.
3. Cute pic, but again, the toy is totally blown.
4. My favorite by far. Again pull back just a tad to get all of his feet and the handle of the wagon. Or, better yet, have him cross his legs indian style as perspective makes his feet look HUGE compared to the rest of his body.
5. Face is flash washed, and his shoulder is cut off. The window is a bit distracting, and it looks like a small amount of camera shake is softening things up.
Overall, if this was just an impromptu session, and some of your first work, I think you did an excellent job. Your eye for composition shows promise with a little bit of tweaking. I suggest a reshoot with this family, make it outdoors in early evening to get some softer light and so you don't have to worry about controlling a flash.
So good job, and keep shooting!!
Hope that helps!