Wow... great question.
I think that every piece of philosophical wisdom that has ever been uttered can ultimately be boiled down to something as simple as, "Embrace life." Not your own life, not even the life of your own species - but all life.
To most rational adults, this concept is probably extremely obvious. Yet, I find that keeping it at the forefront of my conscious mind as much as possible keeps me from thinking in a selfish way - it diminishes the ego, you might even be able to say.
So, to answer the original question, I suppose this would be my parental advice. Although the advice to "question everything" is less abstract, and a tempting answer indeed...