> Is it hedonism if a child-free adult gets fulfillment out of nurturing...

How many people in the developed world are really doing that? My social circle is largely child-free into our thirties and forties, and the big motivation is so that we have time for our hobbies and for travel. Almost no one is dedicating their time to altruism. Especially considering that I live in a long-running welfare state, where helping people in need is generally left to the state and private charity is rare (and often has dodgy religious-sect connotations).