Simple answer: Because vibrations are magic and at no time was that ever more evident than when the piano was a new invention.
Unlike every other extant keyboard instrument that one rang. To our ears, accustomed as we are to the massive ringing of the modern piano, the fortepiano* is almost as dry as the harpsichord. But to ears accustomed to harpsichord the newly invented fortepiano would have seemed extreme in its capacity to resonate. This would have been more than enough to trigger the huge outpouring of music with and for the piano: sympathetic vibration so rich and so varied that it cannot be electronically synthesized.
If you want to get your children interested in classical music (Haydn, Mozart, et al) better to get them intrigued with real resonance--tiny brass bells, finger cymbals, or a triangle--than to imagine that they will gain much by listening to recordings. The ear will get there in its own time.
*Fortepiano, as the invention was initially named, means literally "loudsoft."
