A Brooklyn grandmother unloading groceries was viciously mugged by a young thug as her 4-year-old granddaughter watched in horror, cops said last night.

The 68-year-old victim was approached from behind on Slocum Place, in Kensington, at 9:45 p.m. Wednesday and pistol whipped several times in the head by the punk.

The suspect, described as being between 15 and 20-years-old, grabbed the victim’s cell phone, pocketbook and cash and fled on a black BMX bike.

The woman was taken to Kings County Hospital in stable condition. The child was unharmed.