As adults with children, we know that at some point there will be more than one child at the piano and that they will argue over who gets to play or what they will play together.
Just about every piano can play mezzo forte or mf. It’s not all that difficult to get a piano to sound as loud as the resonant body will allow. It’s all in the power you can put behind the articulation. The challenge with a piano is creating a soft, intimate sound.
Many upright pianos and even some grand pianos use only the cast iron plate as a termination point for the speaking length of a piano wire. That particular metal is very hard and brittle which does well enough for enhancing the bright timbre of a note but can be unforgiving when you’re trying to achieve a deep, dark tone.