A nice charming small game, it could use some save points or multiple lives for the longer levels and the wind door openers could use an animation rather then just flashing to imply that it is spinning. The colors and music are relaxing- I feel like you could implement some kind of atmospheric story told by the environment or by the enemy type and placement- you can add little things to create a nonverbal story that adds to the players curiosity- making them want to clear more levels to learn more about the world and why this kid is collecting batteries.
Another thing that could help is if you made the "you died" screen a lot shorter, so the player can immediately get back to trying again, rather then being faced with the fact that they messed up and now have to wait a few seconds to give it another go- slow screens like that make dieing feel more frustrating rather then a welcoming challenge to try again.

Cuuuute

dat mouth shadeing tho

I really like the stylized way you drew your characters and that amazing cel shading, but it's a bit hard to tell what is going on in the hand area- and to differentiate the pink character's body from the background. The background colors are a bit too similar to the characters- it takes away from the main focus of the main characters and the POP