I scrolled through all the policy headers in the Project 2025 Wikipedia article, and didn’t find anything like this. If anything, my impression from Project 2025 and aligned people is they want the “right kind of Americans” (conservative married Christian whites) to have many more children than they currently plan to.

What you might be remembering is the way Project 2025 and aligned people make references to Social Darwinism themes. One example article covering this: https://worldcrunch.com/in-the-news/rfk-jr-health-agenda-german-view/

“A very central concept of social Darwinism,” says Roelcke, “is that of contraselection.” This refers to the idea that social measures and medical care in a society override natural selection. And according to social Darwinists, this is a highly problematic behavior in modern societies because it leads to so-called degeneration.

“Social Darwinism,” says medical historian Roelcke, “is about taking away social support or access to medical care from the weak, that is, the sick or vulnerable, and leaving them to fend for themselves.” The fact that they then died earlier was not only of no concern to the Social Darwinists, but even desired.

Kennedy’s handling of the largest measles outbreak the U.S. has experienced in decades clearly shows echoes of social Darwinism. Namely, when he falsely claimed that no healthy children were dying from measles and that poor nutrition played a role in the deaths. RFK Jr. is saying between the lines that it’s not the healthy, the fit, and the strong who are dying, but only the weak.