Give your child a shoelace with a stiff tip and a bowl of large pasta tubes.
Show one threading motion slowly: hold the pasta still in one hand, push the lace through with the other.
Tie a knot at the far end first so nothing slides off. Let them fill the whole lace — the repetition is the training.
Threading needs the two hands to do entirely different jobs at once — one stabilising, one acting. That asymmetric division is harder than it looks and underpins every later two-handed task from cutting to tying laces.