basically, if you're going to teach piano to your own kids, set aside a time for it and be serious about it. Keep distractions away, set a time and treat it as if you were sending her to lessons (i.e. don't set other events for that time, it's LESSON time)
This piano represents Kurtz's talent as a musician. The fact that Kurtz is knowledgable about music is made clear on a visit from Kurtz's cousin: "Incidentally he gave me to understand that Kurtz had been essentially a great musician" (Conrad 151). This suggests that before coming to the Congo, he was a civilized and cultured man.