I guess to start off their heads could maybe stand to be a bit bigger or rounder, very slightly though. I say this because with the rest of the the chibiness, it's sort of odd to see well-proportioned heads. The angles of their faces' features are very well done and although a few things are off on size, in chibi form it looks fine (in fact very cute, so well done there).
I suppose another thing could be Haibara's kunai is at an odd angle. From the pose she's in, it seems it'd be facing the camera (her hand is also in position for it) but it looks more like a view from the side or facing away.
The last thing I could say about Haibara is that...well, if she's Haibara she would be smaller in stature than Ran. It's not that much of a tip since this is chibi, but this chibi style looks semi-realistic, so I thought I might as well throw it out there

The last thing overall would be Ran's pose. It looks fine, don't get me wrong, it's just if she got tricked by the log thing, she might be looking the other way more, neh?

Surprisingly I did pretty well here for length (usually the crits I do are longer xD). Very good points: I love the style of these chibis. The thin limbs, the bit of cubbiness in their torsos and their piercing eyes~ Overall, a great (and cute) picture :3