Gather containers that nest — measuring cups, food tubs, stacking cups — and muddle them on the floor.
Ask your child to fit them all inside each other. Let them discover by trying rather than by being ordered.
When it fails because two are the wrong way round, do not intervene. Wait. Undoing and retrying is the part that builds the ordering.
Nesting forces every item to be compared against every other, which is ordering by size done physically rather than abstractly. The container either fits or it does not, so the feedback is immediate and needs no adult judgement.