The crooked background boards in the fist shot are a bit distracting from her...the background draws a lot of attention due to the angled lines. Same to an extend in the second, although the angle has been minimized somewhat. The yellow background with the light fall-off at the top making the bottom pale, and the upper left corner the most saturated is not appealing, and I LOVE yellow backgrounds, either gelled, or real yellow paper. I do not like the look of the yellow's gel-fade...the pale lemonade color at her level and then the strong color at the top is, again, distracting. I do enjoy plain, straight photography, without a lot of effects, but on this kind of studio work, for me, solid technical values are very important.
From a technical standpoint, the yellow one is the worst violator of solid fundamentals: the gelled flash has been placed off to the side, and low, and the fall-off makes it very weak yellow at the bottom of the frame; we can see the gray paper line across the bottom of the shot, then the pale lemonade color, then a bit darker on the left side, but the right hand, close side, is still very light 7/8 of the way up, them BOOM! it transitions. I've seen this done of real yellow paper before, and it looks nice with a black outfit as a counterpoint. This is a case where a different light placement would really have helped: ideally, a gel-fitted strobe clamped right to the back of the chair, or two (yes, two, identical) flash units aimed at the backdrop form 40 degrees or so, to make an even, smooth yellow backdrop color.
The kid is cute, but I think the challenges you are facing might be due to a really small set, and maybe not the room to make the light more even. At close range, or with the wrong type of flash, getting a broad and EVEB gelled color backdrop is tough or impossible. Having MORE space makes it easier to get a wide area lighted with less fall-off, using normal kinds of lighting equipment. On a small set, with a narrow background when the lights are close, the inverse square makes for RAPID fall-off in light intensity; being able to pull the lights farther away mans the fall-off is much more gradual.