Two of them--my brother's son and my sister's daughter--actively dislike children, so I don't see them changing their minds, though my sister, who I think wants to be a grandma, thinks her daughter might decide to procreate if she marries the man she's been dating for years. I OTOH could see my brother's daughter and my sister's son possibly deciding to eventually be parents; the niece likes kids enough to work as a pre-school teacher and the nephew has a soft spot for the kids of his friends. But all of them have, at one time or another, expressed reservations about bringing children into an already messed up world stretched thin on resources. I absolutely would love, and spoil, any great nieces or nephews if that happens down the road but I also completely understand, and respect, all of the niblings' choice at the moment to remain child-free.
Incidentally, all of the niblings are over 30, with the boys both pushing 40, so all have had plenty of time to think about their choices.