[mpipes]

This reminds me of a situation I put my PCs in where the child in question was a really cute Russian girl (looked about 12 but was actually 15) that was 1) a complete psychopath and 2) was a KGB trained agent sent on a mission to release a genetic-engineered Ebola strain into the Vistula intended to create a "no go" hot zone separating the USSR from the rest of that part of Europe.

There were all kinds of hints dropped to clue in the team that this girl was the baddest of the bad. I even had this girl actually murder a fairly harmless NPC that had discovered the vials of virus in front of the team and they still did not get it!! They delivered their little precious, innocent orphan to the kindly priest in Cracow, and I gave them one more chance as she dropped the pouch with the vials getting out of the HMMWV. One of the PCs picked up the pouch, made the roll so he knew vials were in it, and he promptly handed the pouch right to her.

As we ended the session, I took a time out, had everyone make a roll to see if they caught the plague (everyone did) and see if anyone lived (one did).
Then told everyone that was dead that they were dead and why as the resulting Ebola plague made much of Poland uninhabitable and the Poles all but extinct as 90% of the population died!!

As tempted as I was to go ahead and end the campaign and just start over with them running new PCs, I finally decided to take mercy and do a Dallas and let everyone pretend it was just a dream, but they never took NPCs at face value again and paid attention to clues.