I'll take piano music over a crying child any day of the week

Put headphones on the infant?

If it's just piano then it's basically Muzak. The bus itself may even be playing some imperceptibly which you can harmonize with.

I've tried headphones with babies before and it's hit or miss. One would howl instantly if you put them on him while another loved them.

Seems like you found the least intrusive way to keep your kid calm, which I think most people will appreciate.