Ekram ul Haque, 67, a retired care worker was attacked when he was returning with his five-year-old granddaughter from a south London mosque.
Three boys, aged 12, 14 and 15, have been charged with assaulting Haque.
The 15-year-old boy, who attacked Haque was linked to incidents of assaults on two elderly South Asians in Tooting a week earlier.
Graphic images caught on CCTV showed that all the three attackers were black and wore hooded tops.
Scotland Yard confirmed that the assault was being treated as 'racially motivated'.
Following the attack, there was growing tension in the local community.
Haque's 35-year-old son called the attack 'mindless violence' and urged people to remain calm.
"I would urge people in our community to remember that Islam is a peaceful religion and does not condone revenge attacks. If you want to do anything, just pray," he said.