I think that the idea is pretty fun, would be cool if there was a way to implement 2 player into it! The art is cute, and so is the idea. The music fits pretty well too!
One major sort of thing was the horizontal collision on walls - if you jumped into a box you were trying to push and didn't get high enough to make it, you'd get stuck against it while still being able to push it. In fact, if you jumped into any wall whatsoever, you'd get stuck against it until you tried to move in the opposite direction. Made the experience a bit more janky, and also caused a bit of a glitch. On level 4 of the medium difficulty one (Connor and Richael) I ran into a glitch where I shrunk and tried to make a jump. Ended up catching on the side of a wall while shrunk, falling, and respawning over the hole, so there was no way to progress.
That aside, great game!