I hugged my 5yo kid yesterday and said "I love you sooooo much, I whish you would never grow up". And with a genuine smile uttered the following word: "But who is going to take care of me when you die? and how can I have my own kids if I don't grow up?".
So simple, clear and concise; it was the end of the debate. That is the evolutionary answer "Survive and reproduce". I don't think my kid was thinking that deep but it the idea is certainly there, hidden and passed along approprietly.
