The classic example is killing Hitler, with there being variations from assassinating him in the 1930s to actually killing him as a baby (unsettling though that idea is).
I find that people usually project out the major historical changes this would cause while assuming the same people would mostly continue to be born unless there was some clear major effect preventing this. I disagree. I think if you went back and assassinated Hitler after he became a well-known world leader, and then went back to the present*, they would find that virtually no one born ten months or more after the assassination would be the same person. Sure, many of them in that initial period would be born around the same time to the same parents, arising from the same maternal egg their alt-universe counterparts did; but to be the exact person you are requires your parents to have a very specific life course right up to the moment of intercourse, and for the man to ejaculate at that exact moment in that exact position. To read about such a dramatic event would change that at least slightly for almost everyone fairly immediately, I believe.
If the assassination were achieved in infancy, and undertaken quietly and in an unobtrusive way people marked up to natural causes, you might find when coming back to the present that there were genetically identical individuals born months or maybe years afterward. But decades? I doubt that very much, as changes ripple quietly outward.
*To avoid paradoxes including the possibility the time traveler/assassin would have their own birth negated, we’ll assume that they go back to the 21st century, but in an alternate universe instantly created the moment they arrived in the past.