The radiosonde carries all the sensors attached to a weather balloon to measure the various parameters that affect the weather of a place. Since I explained that it was almost like a black box (mostly pre-packaged with all the instruments tucked inside), the child was intrigued by how a closed box could measure the humidity of the air outside ?

This opens up a whole new area of the how humidity sensors work and the principle behind them! Maybe one of these children will come up with the next generation of radiosonde someday!