The nine adults were sentenced to five years in jail each while the three minors were handed down three-year sentences for the April 2012 attack in a Shiite suburb of Manama.
The jail terms are the latest to be handed down to Shiites accused of violence in the Sunni-ruled Gulf monarchy.
A Shiite-led uprising to demand democratic reform was crushed in March 2011 but protests have continued in Shiite villages and districts around Manama.
At least 89 people have been killed since the protests began, according to the International Federation for Human Rights.
Strategically located across the Gulf from Shiite Iran, Bahrain is home to the US Navy's Fifth Fleet and is an offshore financial and services centre for its oil-rich Arab neighbours.