The kid was still being consumed by trauma. They did left him/her (not clear yet) there thinking about his/her safety, but it was premature. At least it would've needed a hell lot of talk and convincing before that, for him/her to understand that it didn't have anything to do with that. And, liking it or not, ultimately the decision was to be made by him/her.
It's sad if the kid actually did end up messing with dark magic because of this mistake. Not the party's fault per say, but it will leave a sorrowful taste on the mouth