Well they've let the Buffy-raping mutated swimteam go in Go Fish, the magic shop owner killing Spike go in Lover's Walk and Angelus just walk away at the end of Innocence, Eric and Chris are the least of their worries
Well, with the mutated swimteam... I suppose there's no proper way to deal with criminal, presumably non-sapient fish-like creatures...
But I don't remember if they ever said what happened with the coach - it was implied that the 'boys' raped him, but did they also eat him?
Buffy letting Angelus go was a major plot point and had huge consequences. As for Spike... hm, Popular Character Immunity?
It's not like they could kill Eric, since he was human, and reporting him to the police would have required a lot of explaining... but I hope that Buffy threatened to beat him up unless he went into therapy. Which reminds me, those 4 kids from "The Pack" must have needed lots of therapy after they ate the principal...