Assuming he puts RFK Jr. in a position of authority, children will die. But he might not do that. Talking about it may have been a way to satisfy his anti-vax base. Trump himself was always a vaccination booster. Recall Operation Warp Speed, plus speaches given early in 2021 where he talked up vaccination, pointed out that he got his COVID-19 vaccination, and encouraged others to do the same. He was booed, so he never mentioned it again.