Congrats on finishing the PJP game jam and continuing to work on it. Your stated concept is intriguing: "seeing through the eyes of a child", but I feel like you haven't yet executed on your promise.
Perhaps you could expand on what looks or feels different through the eyes of a child. For example, one of your core mechanics appears to be changing the gravity of crates when you switch to a child, but it's a tough sell for me. What if instead, the crates turned into balloons when you switch perspectives? Or another idea would be that everything looks bigger when you're a child so what if the crates were larger crates when you switch to the child? If you're intending for the concept (rather than specific gameplay mechanics) to make your game special, I'd spend time listing out all the different ways kids see things differently from adults then build your mechanics around those ideas.
Player movement feels good. Pushing the crate up slopes doesn't feel great though, there's too much friction up slopes which can make them tedious to move. Also, the physics simulated crates can make it feel unpolished when using the crates on the catapult. Try locking the crate's rotation when on the catapult to make it feel smoother.
Nice work on the tileset. The gopher is cute! I like the bobbing idle animations too.
I don't understand why you need stamina in this game. Perhaps you're planning on using it later, but I feel like implementing limited stamina in a puzzle game can make it feel frustrating. Although, I ran out of stamina as an adult and there were no apparent consequences.
Lastly, regarding the puzzle design. It is fairly good, but the communication of mechanics is sometimes unclear. In particular, why can objects move through certain floor tiles in one direction, but not the other (i.e. the one above the catapult)? The tile should be clearer about which direction objects can flow through it to minimize player frustration. Same goes with the ground tile and lasers next to the gopher; it's unclear what the rules of the game are from the visuals.
Overall, good effort. My advice is to be crystal clear on your concept first and make sure your executive aligns with your concept so that you don't continue working on mechanics that you might have to scrap later.