Why should it matter that children be made aware of dissonance?
The power of the individual's response to sound lasts a lifetime. It has nothing to do, really, with the ability to play a piece. Without responses to the individual sounds that make up the piece the action of playing is of short-lived importance, if of any importance at all. I recall getting bored pretty quickly with pieces as soon as I had "mastered" them.
I notice that when children are encouraged to savor their feeling about sounds they do not lose interest in the music: quite the contrary, their love grows and grows.
One of the most startling instances of this is a radically challenged young man whom I have taught since he was seven. Now in his early twenties, blind, autistic, and intellectually challenged, he knows and loves some incredibly sad pieces by Bartok: pieces that require of him a subtlety of touch and coordination to which he otherwise lacks access.
The other day at his lesson I was moved that he could produce the touch and articulation that made one chord progression seem to weep. I told him that he had just done something so beautiful with his hand that I will never forget it.
I told him that some people live their whole lives and never do anything that beautiful with their hands.
He needs to know that he did it, that he can do it again, that it speaks for a capacity that he cannot access by himself or express in any other way. Why does he need it? Because for all his disability, for all the trouble his life is, he is a human being as subject to feeling as everyone of us.