Both boys were taken to Aberdeen Royal Infirmary with serious burns following the incident in the city’s Granitehill Road in the Northfield area, the Aberdeen Evening Express reported.
Police are searching two youths who were thought to have been wearing dark clothing and gloves at the time of the incident between 8pm and 8:30pm.
A Police Scotland spokesman said: “Police Scotland is appealing for information after two boys were assaulted in the Northfield area of Aberdeen.
“The boys had a substance thrown at them which caused burn-type injuries.
“The area where the incident happened has been cordoned off to allow the scene to be examined.”
Detective Inspector Allen Shaw, who is leading the investigation, said: “This has been a shocking and despicable incident against two young boys who have obviously been left upset and shaken by what has happened to them. They have been left with significant injuries and were taken to the Royal Aberdeen Children’s Hospital for treatment.
“Extensive inquiries are ongoing to trace those responsible and we are working with our colleagues in the Scottish Fire and Rescue Service as part of our investigation. There will be a police presence in the area for some time, however the scene where this incident happened has been examined and I can assure the public it is safe.
“I would appeal for anyone with information about the incident, whether you were in the area at the time or know anything about it, to please get in touch. You can contact Police Scotland on 101, via the Police Scotland website or via the charity Crimestoppers on 0800 555111 if you would prefer to remain anonymous
“I can assure the local community that all resources available to us will be used to trace those responsible. It won’t be tolerated.”