What a brilliant game! Characters and music are adorable, and the puzzles are interesting and challenging.
The cannons should be solid objects- I kept trying to jump onto the cannon in level three before realizing that it was just in the background. Being able to walk through them from behind and get shot is kinda strange as well.
I particularly liked level four, which was fun to figure out and introduced several mechanics with zero words. Well done!
I like that detaching causes Olly to jump, and I was super happy when I found out the mechanic is used in puzzle six (I think? The level with the tiny door for Timmy right at the start. That door's hitbox also sticks out from the wall and can be climbed on to make the jump btw)
I definitely would like a more noticeable indicator of which character you have active- the cutest and easiest would be to go Snakebird's route and have the inactive critter close its eye(s).
All in all this is a fun, original game which strongly adheres to the theme. Full marks!