Police said the boy broke into the home and woke the sleeping girl, raping and stabbing her more than 30 times.
The girl's 18-month-old brother woke up during the attack, prompting the suspect to also stab him more than 10 times, police said.
Police Sgt. Denise Quatman says the suspect eventually fell asleep, giving the girl an opportunity to grab her brother and escape. Both were taken to a local hospital, where they remain in critical condition.
When police arrived at the scene, they found the suspect asleep. Police are waiting for tests to determine if he was under the influence.
He's being held in juvenile hall on suspicion of attempted murder and sexual assault.
The Associated Press contributed to this story.
