(New 52 bridge from Flashpoint.)
Professor Zoom didn't kill Barry's mother.
It was just an ordinary burglar.
But Barry f####d over time by saving her.
Zoom was just immune to the changes to the timeline because of his connection to the speed force, and he laughed, oh how he laughed to see that the great and wonderful Flash destroyed the world so much just because he needed his mommy.
What Zoom did later on was trying his hardest to stop Barry from reversing his mistake, so that the Flash would be remembered as the worst asshole villain ever.
Not sure what happened in all the older "renditions" of the DCU, I grew up with Wally, but in the "arrowverse" young Barry encountered a blur that used wind to throw him across the neighbourhood... Time travel was most certainly implied that he himself was there or a villain was trying to kill the Flash before he became the Flash.