First let me ask you this ?
Is the child a boy or a girl ?
Their are different feelings and different ways of handling with the phsycological.
Every boy/man wants to know that someone out their is the least bit interested in him.
He does not want to feel alienated every time he looks in the mirror or when he sees another guy with a pretty girl and wondering why he cant have the same.
For me I delt with it the wrong way. I actually dropped out of college and cost myself a ton of money simply because I was listening to my inner voice. I thought about the situation too much.
It probably was not as bad as I made it seem.
Never the less, no matter how much you try to tell him that its not that bad. He will not ever accept this unless it is no longer on his face.
When he is able to look in the mirror and not see the acne, then he will feel better about himself.
To make a long story short, get the acne treated and cured. Then the phsycological aspect will take over on its own. You will not really have to do much, but some simple compliments.