Having someone who is dependent on you definitely makes you important, whether that's kids or your dying grandmother or something else. But creating that dependency explicitly as a means to feel important is just weird.

"I have a hard time to see any relevance in a life without children anymore."

Consider the fact that Chinese slaves made everything you own, and are wearing. Isn't that worth caring about? Wouldn't it be "relevant" to try improve that situation?

In this person's mind, a person without kids who is trying to solve the problem of human slavery, is living an "irrelevant life". It goes to show you how stupid the average person is, including the average parent.