This isn't just silly, but can actually be dangerous. The "checkpoints" we have for learning are determined by our third-party mental model of that activity, no

This isn't just silly, but can actually be dangerous. The "checkpoints" we have for learning are determined by our third-party mental model of that activity, not by the first-person experiences of the learner. A child will learn to do something when they are mentally and physically prepared to do it in the first person, when a whole variety of variables we have no awareness of align. Even something which may appear isolated from other areas of development (walking, talking, holding a spoon) is an extremely superficial heuristic for the development of millions of interconnected systems within a child's body.