
First you use 98 colors for those.
Try to restrict your colors first.
Use ramps with equal amount of colors and good contrast in them. YOu always can change colors in the process.
Consider the color of the outlines. You use dark blue for the trrousers, dark red for the pullover, why do you use black for the head?
Then the characters stand there very stiff, you could add a lot more weight to the poses. YOu could add depth, depending on how the character is places in space.
next thing is that a saturated red like this might not be the best combination with the the blue trousers.
You always can add more colors and go crazy with details.
Don't forget to add hair, it adds a lot of character at this size.