Gather six objects from two obvious groups — three things you wear, three things you eat with.
Muddle them up. Put one of each group in front of you as headers, then hand your child the rest one at a time.
As each one is placed, say the reason out loud: 'the spoon goes here, because we eat with it.' Let them place it wherever they like and give the reason anyway.
Grouping by function rather than looks is the beginning of categorical thinking, and categories are how vocabulary scales — a child who knows 'things we eat with' can absorb 'fork' far faster than one storing every word separately.