Looking at London has a page about these little blue people but even there we can find no origin story explaining why and when the first such statues were erected. We note that there seems to be a rule that the boy is on the left and the girl on the right, just like the TV breakfast show hosts. When that row blew up the TV studios admitted that the left-hand position has always been seen as the senior spot, due, apparently to how the eye moves when reading.
Christ's Hospital was known as the Bluecoat School but there are no little blue people that we could see in Newgate Street. However we understand there are more statues inside and also in St Bride’s church Fleet Street and in the galleries at the Museum of London.