Sergey Koudryavtsev stabbed his parents at their Kensington home.
The little boy was stabbed last week in Wallsend, Newcastle.
A 29-year-old man was killed.
Peter Duncan was attacked in what police said was an unprovoked “chance encounter”.
No arrests have been made.
A murder investigation has been launched and police are working to track down those involved.
The killing is the 29th fatal stabbing in the capital so far this year.
A Section 60 order is in place for the whole of Hackney.
Gavin Garraway died near Clapham Common tube station.
“He’s not lived his life yet.”