It's an interesting design but I feel like you focused on your renders and presentation more than the design itself. For one, the front wheel doesn't turn? Are you expecting the flex of the material to be enough to steer the bike? It won't want to lean because of the cylindrical tires - and while I could see wider tires helping to make it easier to stand up, that kind of defeats the purpose of the balance bike which is their feet are used to balance it while they get used to turning and distributing their weight.
I'm also curious if you actually gave your prototype to any children, the sheet material used makes me think the handle areas would wind up being extremely uncomfortable since you are asking them to lean or grab on the flat edge of the sheet.
It looks like most of the work went into the renderings, which I suppose is OK if that was the goal of the project for you - but I would revisit some of the ideas and try to prove they were good design decisions, not just aesthetics for renderings.