It happened in the Galgorm Road area of Ballymena this afternoon, Thursday, April 12.
The PSNI say the boy sustained facial injuries after being struck in the face by a male youth armed with a hammer, at around 3.30 pm.
He is receiving treatment at hospital.
Two boys aged 15 and 16 have been arrested in relation to the investigation and are currently in custody assisting officers with their enquiries.
The investigation is ongoing and officers would ask anyone who witnessed the incident or who has any information to contact them in Ballymena on 101 quoting reference number 755 12/04/18.
Alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111 which is 100% anonymous and gives people the power to speak up and stop crime.