I didn't want them to get thrown into jail, and they won't be. Just the other day some teens (not the ones who killed the fish) beheaded some chickens to see if they'd run around with their heads cut off. All they had to do was clean the chicken coop for a little while and read a book on animals' feelings so that they wouldn't do that to animals again.
I think that they need to be told that it's illegal to do what they did, but anyway it's not considered animal cruelty to kill goldfish. However "teens will be teens" doesn't apply to everyone.
Everything's been taken care of though, the teens won't torture fish again, and at the next VBS I'm going to make sure that there isn't another fish pond.