Police are describing the death of a four-year-old girl in Grimsby as "unexplained".
Poppy Widdison died at the weekend after being transferred from Grimsby to Sheffield Children's Hospital.
Two people have been arrested.
More top news
Paul Dadge become the unwitting face of the 7/7 rescue effort after a picture of him helping a woman in the aftermath went around the world.
London was in a celebratory mood on 7 July 2005, but everything changed when three suicide bombers attacked the capital's transport network.
A list of commemorative events as the UK marks a decade to the day 52 were killed and hundreds injured in London terror attacks.