Always thought that a minimal effort "Stop Hitler As Early as Possible" would be to kidnap him in Austria at about 1 year old, have him circumcised, and leave him in the Jüdisches Waisenhaus (Jewish Orphanage Berlin-Pankow) in Berlin....alternative ideas...
Adolf Hitler ceases to exist, and an innocent child is given the chance to grow up.
Of course, there's enough cultural anti-Semitism without him, and the anti-Versailles resentment would still be a thing, so no bets on avoiding WWII.