I wouldn't kill him. One, it would be murder. Murder of an innocent child. At that point he had done nothing wrong, he was completely innocent. If we had captured him after the war, I would have had no problem putting him on trial and excuting him for his crimes, but I just think killing him as an infant would be wrong.
Also, as has been pointed out, it was the experiences in WWI and in inter-war Germany that really shaped him into what he became. For all the evil he actually did he did have the potential to do great good. In fact, he did do great good. He quite literally saved Germany, and got it back on it's feet and functioning again. He also invested a lot of time, energy, and money on scientific development and breakthroughs as well things like arts and cultural. Our world would not be what it is today if it wasn't for Adolph Hitler. We can argue all we want about whether it would have been better or worse without him, but all in all I rather like our world, even with all it's problems. Even WWII itself, as horrible as that conflict and it's aftermath have been have, has helped further human developemont. In fact it is in large part because of Hitler that I have such a great love of Germany and it's people. It's been my study of the Second World War that is really helped develop my interest in Germans and Germany.
Also, you guys might want to look up Command and Conquer: Red Alert and it's setting. The premise of it's plot line is that Einstein discovers time travel and uses it to eliminate Hitler from the timeline, much like we are discussing it here though with different circumstances. Long stary short, the absence of Hitler to provide powerful opposition to his fellow dictator Stalin means that communism spreads through an alternate world war. I can't explain it to well here, but I think it does provide some food for thought about what would happen with Hitler's absence from history.
"I reject your reality and substitute my own" Adam Savage

You can run, but you'll only die tired.
