The bombings at three churches in Surabaya -- claimed by the Islamic State group -- were the deadliest in years, as the world's biggest Muslim-majority country grapples with homegrown militancy and rising intolerance towards religious minorities.
The bombers -- a mother and father, two daughters aged nine and 12, and two sons aged 16 and 18 -- were linked to local extremist network Jamaah Ansharut Daulah (JAD) which supports IS, said national police chief Tito Karnavian.
The mother, identified as Puji Kuswati, and her two daughters were wearing niqab face veils and had bombs strapped to their waists as they entered the grounds of the Kristen Indonesia Diponegoro Church and blew themselves up, he said.
The father, JAD cell leader Dita Priyanto, drove a bomb-laden car into the Surabaya Centre Pentecostal Church while his sons rode motorcyles into Santa Maria church, where they detonated explosives they were carrying, Karnavian said.
"All were suicide attacks but the types of bombs are different," he told reporters.
"This is related to JAD -- Jamaah Ansharut Daulah."
The group, led by jailed radical Aman Abdurrahman, has been linked to several deadly incidents, including a 2016 gun and suicide attack in the capital Jakarta that left four attackers and four civilians dead.
That was the first assault claimed by IS in Southeast Asia.
Police on Sunday said four suspected JAD members had been killed in a shootout during raids linked to the deadly prison riot this week.
Five members of Indonesia's elite anti-terrorism squad and a prisoner were killed in clashes that saw Islamist inmates take a guard hostage at a high-security jail on the outskirts of Jakarta. IS also claimed responsibility.
East Java police spokesman Frans Barung Mangera confirmed the deaths of 11 people with 41 injured in the coordinated attacks at around 7:30 am (0030 GMT).
Images showed a vehicle engulfed in flames and plumes of thick black smoke as a body lay outside the gate of Santa Maria Catholic church, with motorcycles toppled over amid the mangled debris.
In addition to the suicide blast police experts defused two unexploded bombs at the Surabaya Centre Pentecostal Church.
Indonesian President Joko Widodo slammed the attacks, telling reporters: "We must unite against terrorism."
"The state will not tolerate this act of cowardice."
Nearly 90 per cent of Indonesia's 260 million people are Muslim, but there are significant numbers of Christians, Hindus and Buddhists.
Concerns about sectarian intolerance have been on the rise, with churches targeted in the past.
Police shot and wounded an IS-inspired radical who attacked a church congregation outside Indonesia's cultural capital Yogyakarta with a sword during a Sunday mass in February. Four people were injured.
In 2000 bombs disguised as Christmas gifts delivered to churches and clergymen killed 19 people on Christmas Eve and injured scores more across the country.
The archipelago nation of some 17,000 islands has long struggled with Islamic militancy, including the 2002 Bali bombings that killed 202 people -- mostly foreign tourists -- in the country's worst-ever terror attack.
Sunday's bombings had the highest death toll since nine people were killed in 2009 attacks on two luxury hotels in Jakarta.
Security forces have arrested hundreds of militants during a sustained crackdown in recent years that smashed some networks, and most recent attacks have been low-level and targeted domestic security forces.
But the coordinated nature of Sunday's bombings suggested a higher level of planning, analysts said.
"Recent (previous) attacks have been far less 'professional'," Sidney Jones, an expert on Southeast Asian terrorism and director of the Jakarta-based Institute for Policy Analysis of Conflict, told AFP.
The emergence of IS has proved a potent new rallying cry for radicals, sparking fears that homegrown extremist outfits could get a new lease of life.