Some poskim say that a minor may tie tzitzis even for an adult (see Artzos HaChayim cited by Mishnah Berurah 14:4), as long as he is being supervised by an adult (gadol omed al gabav). Does this mean that the supervisor must watch his every move, or is it enough if the supervisor is just generally keeping tabs on what the minor is doing?
What the minor is doing can be verified by a sight check after the fact (similar to your verification above). The gadol is there to make sure the tzitzis are tied lishma, which a minor may not be thinking about (or know about). I think we can agree that the gadol needs to prompt the katan to perform the initial knot on each set lishma. The rest of the knots and windings don't need lishma. They don't even need a Jew. (The Mishna Brurah 14:1 says a Jew must do the placement, the 1st knot and the 1st chulia. I'm not sure if they all need lishma.)