When teaching music, especially to children, the notion that a
note has really
doesn't have two separable aspects is often lost: its
pitch and its
duration.
In the world of musical theory we can, and quite often do, have pitches without duration, and durations without pitches; in the real world of heard sound, we cannot.
This quite commonly leads to the student claiming, "just let me learn the notes now, and I'll learn how long they last latter." But what happens is the student learns the pitch without the duration. And trying to teach the correct duration after is often an incomplete process.
This is one of that most difficult aspects of teaching piano, and I presume any other instrument.