The boy, Ali Gawad Ahmed, was killed after a tear gas canister used by police to disperse a protest went off near him Wednesday in Setrah, Bikya Masr reported.
Bahraini Shiites have been protesting since February for reform by the ruling Sunni monarchy.
Thousands of people gathered in the streets of Setrah Thursday before the boy's funeral, CNN reported.
"People are more upset and angry than I've seen at funeral here before -- I think because he was so young," said pro-democracy activist Zainab Alkhawaja.
At least 30 protesters have been killed by police forces dispersing crowd by using live ammunition, activists say. More than 1,000 people have been arrested and 2,000 have lost their jobs for alleged participation in protests.