At best he showed extremely poor judgment (what would possess you to do this?), at worst he should be going to jail and into a sex offender registry.
All we have is the word of the poster that the recipients were underage, and we don't know whether Dream had reason to know if they were underage. I'm gonna wait and see if more evidence comes out (all I've seen in the thread with the nude, which proves its Dream but is innocuous otherwise, and the audio of his voice, which ALSO doesn't prove anything since school could refer to college as well as anything below that level), but this doesn't look good at all right now.