Children of Earth: Day One - S3-E1
Revealing mistake: When the children are possessed by the 456, they're supposed to be frozen and stare blankly ahead. But during the second possession, as the camera is panning across a school playground, a boy on the far right is looking directly at it. As it moves closer to him, he swivels his eyes back to where they're supposed to be. (00:16:30)
Children of Earth: Day One - S3-E1
Character mistake: Lois says that Colonel Aduya's uniform "isn't British Army". In fact, it is entirely (and accurately) British Army with the exception of the small UNIT badge over the pocket.
Children of Earth: Day One - S3-E1
Factual error: On the government database, Torchwood is described as being founded by HRH Queen Victoria. As a sovereign, she was actually HM (Her Majesty) not HRH (Her Royal Highness).
Chosen answer: As long as Jack's been in charge of it, Torchwood Cardiff has had a different agenda than Torchwood One. Tosh and Owen were there to watch for signs of the 10th Doctor, however, it was the 9th that showed up when the ship crashed in London.
Captain Defenestrator