A spokesman for Scotland Yard said: "The victims - a 40-year-old father, a 36-year-old mother and their two-year-old boy - were found with injuries consistent with a noxious substance, believed to be an acid, being thrown at them.
"They were initially taken to a north London hospital and were subsequently transferred to another hospital.
"The man's injuries, whilst not believed to be life-threatening, are being treated as life-changing.
"The woman and child suffered minor injuries and have since been discharged."
The London Fire Brigade said the adults suffered 15 per cent burns to their hands and bodies while the infant was burnt on his face.
The liquid had a PH reading of one and tests confirmed it was a strong acid and oxidizing substance, a spokesman said.