Bahrain's interior ministry said two children were injured after they were instructed to plant a bomb in the same village where a bomb killed two local policemen and an officer from the United Arab Emirates earlier this week.
The two children, aged 10 and 11, had been instructed by "terrorists" to plant a bomb in Daih, west of the capital Manama, but it exploded as they were handling it causing serious injury to one of them, the statement by the ministry said.
Monday's attack in Daih had raised fears of more violence in the Sunni Muslim-ruled kingdom, where opposition groups led by majority Shi'ites have staged protests for the past three years demanding political reform and an end to perceived discrimination.
Bahrain blacklisted three anti-government groups as terrorist organisations after the blast took place, outlawing the February 14 movement, Saraya al-Ashtar (Ashtar Brigade) and Saraya al-Muqawama (Resistance Brigade).
The little known Saraya al-Ashtar claimed responsibility for Monday's attack in a message on social media that could not be immediately authenticated.
The Ministry of Interior said late on Wednesday it had arrested four more people in connection with Monday's bombing.
Authorities said earlier this week that 25 suspects had been rounded up in relation to the Daih bombing.
"The statements of the (four) detained indicate that their roles varied from bomb making, to monitoring and photography, and it was learned that other key actors were responsible for luring the police to the scene," the statement said.
Bahrain's Shi'ites have long complained of discrimination against their majority community in areas such as jobs and public services, charges that the Sunni-led government denies.
The Gulf island is a US ally which hosts the US Navy's Fifth Fleet. The Sunni al Khalifa family, which has ruled for two centuries, has resisted Shi'ite-led demands for an elected government, not one chosen by the king.