A 10-year-old girl was one of the three injured in an acid attack, the Metropolitan police said.
Police rushed to the scene at a block of flats in the Beaufort Park area of Colindale at around 7.20pm, in London on Monday.
Also, a 36-year-old woman and a 43-year-old man sustained injuries when a corrossive substance was thrown at them.
The victims were rushed to hospital with non-life threatening injuries.
They have since been discharged from hospital.
A motive for the attack has yet to be established.
There have been no arrests.
Detective Sergeant Ewa Czura said: “It is vital that we identify the suspect responsible for this attack and we need the public’s help.
“If you were in the area and witnessed the incident or have any information that could assist, I urge you to come forward and speak to police. The information you have might be essential to our investigation and help to bring justice to the victims and their family.”
Please call police on 101 or tweet @MetCC quoting CAD 6733/12July or contact independent charity Crimestoppers, anonymously on 0800 555 111
Watch the latest videos from Yahoo News UK