Kyle is major character is The Sacrifice but also appears as minor role in The Dead and appears once in The Fear and The Fallen. Unlike most kids, Kyle finds the sickness a good thing.
Kyle is what most of the characters call crazy as he enjoys the sickness that has spread over the world and enjoys killing the adults. He is shown to be very sadistic when killing the sickos.
In The Sacrifice we learn that Kyle suffered from depression before the sickness and that he wasn't very good at school. He hated people like Ed (popular and good looking) and wanted to kill them before the sickness hit.
He admits that before he always wanted to do something "great" like taking a samurai sword or a machine gun and killing everyone in his school then committing suicide so he would go down in history.
He visited a therapist before the sickness.
He appears beside Ed at the battle of Lambeth Bridge when children and sicko's were hurrying away from the fire.
When the remaining kids retreated towards the boat Ed saw that he was alive.
When they hijacked the boat he went to help Aleisha by finding a first aid kit.
He yet again survives the boat wreckage and from then lived in the Tower as Ed's bodyguard.