Fantastic improvements with Littlefoot and Cera.

(I do think Littlefoot’s neck looks a little thick, and was the one thing that I liked better before.) Unfortunately, in Littlefoot’s case, apart from the smaller eyes, I still can’t really tell that he’s supposed to look older, and I’m at a loss for suggestions.

Petrie’s head looks great (I like that you kept a the slight jaggedness he has to his beak), but his body looks rather skinny, and his legs a little long. Overall I think his proportions are a little too human-like. I would suggest making his fingers and toes more pointed (maybe not with claws like Pterano’s; I suspect his design included those to make him look just a little menacing), but keeping them black.
I really like how you drew Ducky. She looks much older, but not fully adult, and still manages to be quite cute.

I might suggest making her crest and forearms (not the whole arm; just the area between the elbow and the wrist) just a little thinner. Also, the position of her tail looks just a little odd; it seems to curl very sharply downwards and forwards (almost to an unnatural-looking extent), and doesn’t look quite sufficient to balance her given how far forward she is leaning. (My proposed solution is rather complex, so please bear with me.

) Right now the position of Ducky’s tail looks like this:
). My suggestion is to bow it further outward, so that the shape of the curve is more of a half-circle than a flattened arch. This would involve changing the inside outline of the tail (the part behind her knee) as well as the outside outline which connects with her back. The top of her tail would slope much less steeply downward from her back, as would the side that connects with her leg. The tip of her tail, meanwhile, would not need to have its shape or position changed at all. The result is that you would make the tail longer, its base thicker (more like Littlefoot's and Cera's in your other images), and its position more realistic.
It occurs to me that perhaps you are working with limited space (possibly the reason you drew Ducky’s tail curving so far forward in the first place), but if you were to only move the outer curve of the tail to the edge of the image, I would think that would be sufficient.