Jason and his mother were trying to protect children[]
The only known kind of people that Jason and his mother killed were Teenagers, Adults, Camp Councillors, anyone who got in their way like law enforcement, and basically anyone who entered the ground of Crystal Lake. Not once have they killed actual children. That's because they're trying to keep children from suffering the same fate Jason did as a child. They fear that if the camp reopened or if children were on a vacation to the lake with their parents, if the parents or the councillors were busy banging each other, they wouldn't notice the children drowning.