First of all, I absolutely love the fact that you've put in Kida and The Spring Sprite in your art. A lot of people tend to forget about them.
The Spring Sprite is the best drawn character in this piece, she looks spot on. Eve also is well drawn, and I like the interaction with the characters.
Your coloring is really well done.
Ariel's upper torso is pretty good, though her tail could use a little work. I feel like the lines would be more wavy and hazy under water rather than crisp and clear. Also her hair is kindof a blob. You might add some minor lines within the hair itself, or even add some chunks and strands at the bottom to make it more defined.
Kida's face looks a bit...fat. Thinning it out and adding some extra shading along the sides to show the raised head should help.