A cute little game, glad I could find my cubs!
As others have said, the double jump is awkward. It seems that to get the maximum height you need to quickly double press the button, as if you're adding together two separate jumps and they somewhat cancel out if they're not "in phase". Usually this would instead work by the second button press starting a whole new jump, with the initial acceleration resetting as if you were just leaving the ground again. If I'm guessing about your implementation correctly, I think you could just cancel the first jump and let the new jump take over.