Children are not the penultimate achievement of humanity. In fact, they're one of the core things that take zero learned skill and can be created and raised entirely via instinctual means.

I would argue that those who leave the most behind are those who are kind and thoughtful to those in their lives. They leave behind one of the most important and precious things that anyone ever could - pleasant memories in the minds and experiences of others. They brought direct happiness to others through their kindness. This is the type of person I strive to be, and I feel enriched and deeply fulfilled when successful in doing so. In some ways, the type of peace that can bring can be one of the few things that you can "take with you" in death, in that you will feel that happiness until your very last moment, which you will most likely not generally do with material possessions.