What it teaches
The instrument families, and the feature that defines each one: strings are plucked or bowed, brass is blown through a mouthpiece, percussion is struck.
This is classification again — the same thinking as the animal groups, applied to something a child hears rather than sees.
What to look for
The piano is the argument worth having. It has strings inside and they are struck by hammers, which is why it is in two families depending on who you ask. That is a real disagreement among musicians, not a trick.