The first incident unfolded at a school in Adelaide Road, Swiss Cottage just before 12.55pm today (March 4).
Officers and London Ambulance Service crews attended and found a 12-year-old boy who had been stabbed.
He was treated at scene before being taken to hospital where his condition was assessed as non-life threatening.
Two 14-year-old boys were arrested on suspicion of GBH and possession of an offensive weapon.
Shortly after at 2.30pm, emergency services rushed to Paradise Road in Clapham following reports of a shooting.
At the scene, a 16-year-old boy was found injured, however, he was pronounced dead shortly after.
Police are working to identify the teenager and contact his next of kin.
Superintendent Gabriel Cameron, who is leading the local policing response, said: “This is an enormously shocking incident which I imagine will cause huge distress to the local community.
“Our thoughts are with the young boy’s family at this devastating time.
“Local officers are on the scene gathering CCTV and speaking to witnesses to piece together what has happened.
“They will be supported by specialist homicide investigators shortly.
“Please rest assured we will work around the clock to identify and find those responsible.”
No arrests have been made at this early stage of the investigation.
A crime scene and cordons remain in place while emergency services undertake their enquiries, which are ongoing.
If you were a witness or have any information, please call police on 101 with the reference 4116/4MAR.
You can also contact the independent charity Crimestoppers on 0800 555 if you want to remain anonymous.
The stabbing and shooting incidents are not linked.