Police and paramedics were called to an incident in Brook's Road, Newham, shortly after 8:15pm.
Officers found the 12-year-old suffering from a stab injury in Plaistow.
He was treated by paramedics at the scene, before being taken to hospital.
A Scotland Yard spokesperson said the victim is still being treated in hospital but his condition is "not life threatening".
Police said two men were arrested and are in police custody this morning.
The men, one in his 30s the other in his 60s, were arrested on suspicion of Grievous Bodily Harm (GBH) and affray.
A crime scene is still in place around the location of the stabbing and inquiries are ongoing to determine the circumstances surrounding the incident.
Detectives have appealed for witnesses, or anyone else with information to contact the police on their 101 phone line.