For the middle one, you should definitely work on defining her face shape a lot more. It looks like she might be a nesting doll or something, since the lines siggest that her chin leads directly into her neck without tapering back at all. I can see where her chin is just fine, but it's at such an unrealistically sharp angle and it doesn't follow through into a jawline and a neck, so the brain takes it for a random line (of which there are legions in your piece) and takes the hairline to continue the face instead. Speaking of the hairline, you could definitely do better here; I can't really say exactly what to do, but I suggest you take some looks at how long hair functions, since right now it's falling around her head in a very unrealistic manner.
The one right above me has, as with all the others, incredibly messy linework, but is solid in terms of form, although his left pant leg seems to be noticeably shorter than his right, and I don't see any reason why it shoud be bunching at his knee like that. If you'd put in the time to clean it up and colour it, I'm sure you'd come out with something very cool.
Out of curiosity, are these works from scratch? I think you could definitely benefit from buying a drawing tablet or using a scanner if you're the pencil art sort.