People always think that if you invent a Time Machine you should kill Hitler when he was a kid. Screw that, the man we really need to kill as a kid is Thomas Midgley Jr… Dude invented both Tetraethyllead and CFCs.
Lead gas is also still in use! There are lots of old planes that take higher octane gas, and because rich people tend to own planes, the government allows aviation fuel to still have lead, leading to poisoning children that happen to live downwind general aviation airports. www.politico.com/…/aviation-lead-fuel-00081641