I think the answer as to why the lighting is so flat has been broached above: the room is small, and there is a LOT of ambient spill in a small, white-painted room, plus the background fabric is a highly-reflective pink. There are two umbrellas on the background, but one of them has more fall-off than the other, and I do not like that all that much in this case, with a light pink-hued fabric background, the dark side (camera right) draws attention away from the subject, the cute little girl. In the first shot, the main light is awfully high up, and her eyes are dull and lifeless, due to lack of a catchlight from the main light.
In shots #1 and #4, it appears that the brightest parts of her dress are blown-out, overexposed. Overall, if you think the lighting is too flat, and it is indeed rather low-ratio, then you need to control the spill light bouncing off of the walls and ceilings. You do not mention what type of umbrellas you are using; shoot-through umbrellas send bout 60% of their light backwards, toward the walls, and 40% shoots through and hits the subject, thus providing a HUGE amount of often undesired ambient spill. Look at the depth of the shadow under the little girl's chin in shot #4---that shadow is getting a TON of fill-in light from "the environment"...probably a combination of the walls,ceiling, and the pink fabric, plus the light from a larger softbox is quite soft and wraparound. The softbox itself, it it is flush-faced and big, is also giving ample light to the set.
It's helpful to describe the size and type of the modifiers; umbrella size and style (shoot through? convertible? silvered, etc); softbox dimensions and brand/style/accessories, etc. Anyway: in terms of how does the lighting look? Photo #2 is my favorite, since it does not have any blown highlights, and it has a bit more sparkle, a bit more contrast, than some of the other shots. Overall, this lighting is not terrible, not is it superb--it's somewhere in the middle. Many people would be happy with these results, but the images do lack the really superior "quality of light" that most people really would love to be able to get. If you want better C&C and better,more-pointed suggestions, you'll need to specify the exact size and type of modifiers used, otherwise all we can do is look and guess; my guess is 1) too much spill light in the shooting area, due to the umbrellas lighting the backdrop.