So here’s the plan: we travel back in fictional time, and save Jason from drowning so that Mrs. Voorhees doesn’t go all crazy. Then, we do some more fictional-time travel, and steal all the slashers at age 5, bringing them to Mrs. Voorhees so that she can adopt them. We will also need to give her lots of money, so that she can afford to raise them. It’ll be like a slasher version of the Evil Baby Orphanage.
It’s true that some potential-slashers (I’m thinking Michael in particular) might end up killing people as they get older anyway, but since Mrs. Voorhees became a slasher herself in an alternate timeline (and therefore theoretically still has the potential to do so in this timeline) she would be understanding; and acceptance is the most important thing.