Children are our only real legacy. The only thing we can leave behind to change the world...for better or for worse. The love we give them, and stuff we teach them, will shape who they are and still be here long after we are gone. Nobody will give a crap how much money you left behind, or how big your house was, or what kind of cars you drove. That will all be quickly forgotten, and you cant take any of it with you when you die. Invest your time, your effort, and your love in your children and grandchildren. Or someone elses, if you dont have kids. Maybe through the Big Brother/Big Sister program or a mentorship opportunity.
To paraphrase:
"The world flourishes when old men plant trees they will never really see... knowing that one day their grandchildren may rest in their shade."