I don't think being a parent makes people necessarily more caring of nature, but out of self-interest, it might.
Maybe parenting forces us to be realists and fuels us with the optimism we need when striving to create a better world and outcome for our children.
Perhaps. Maybe it fills is with the fear of failure in the eyes of our children. No one wants to be a deadbeat dad.
And you are right about what childless people tend to say. They don't seem to actually care about changing the future for a better outcome though.