Why did purple Guy kill the kids?

It is unknown why Purple Guy killed the kids, and Scott hasn't revealed it, and I don't think he will. However, here are some possible reasons:

-Purple Guy hated kids, maybe he had bad experiences with them

-Purple Guy has mental issues and is physiologically messed up

-He was angry and decided to take his anger out by killing them

-He was making kills possibly as a satanic ritual or getting into a gang that required a kill

I really don't know, but number two is the best bet, I would say.