3 ideas
Science kits and lab equipment are expensive, but junk such as used bottles, straws, rubber slippers, and matchboxes costs nothing and exists in every household and village. Building apparatus from trash removes cost as the barrier, so a poor rural child can do real experiments rather than memorize textbook diagrams. Free distribution in many local languages extends the same logic to the instructions themselves.
Each toy is designed so that its working depends on a single principle, such as air pressure in a bottle pump or electromagnetic force in a magnet-and-wire motor. When the toy works, the child has made the principle visible and testable in their own hands. Keeping to one law per toy stops the lesson from blurring into a spectacle with no clear cause.
A used film canister, a refill tube, or a bicycle valve tube is treated as a ready-made component with useful properties such as airtightness, flexibility, or a hollow bore, rather than as waste. Learning to look at discarded objects by their mechanical properties trains a habit of improvised engineering and resourcefulness. The same object can then be reused as a piston, a nozzle, or a pivot depending on which property the builder needs.