A damaged motorbike is seen at the scene outside a church following a suicide bomb
Indonesia is the world's most populous Muslim nation.
Police say the father crashed a vehicle loaded with explosives into one church, while his 2 sons aged 18 and 16 ignited bombs at an entrance to another church.
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, Karnavian said. Two sons, ages 18 and 16, carried out one of the attacks with a motorcycle bomb, and the father used an SUV for his attack.
Investigators believe the parents belong to Jamaah Ansharut Daulah, a terrorist group that lends its support to ISIS in Indonesia, the police general said. Police said the family was among 500 Indonesians who have returned from Syria and may have ties to the Islamic State, Reuters reported.
IS claimed responsibility for the attacks in a statement carried by its Aamaq news agency.
Indonesian President Joko Widodo visited the sites and described terrorism as a crime against humanity.
National police chief Tito Karnavian said that the father exploded a vehicle bomb, two sons aged 18 and 16 used a motorcycle for their attack, and the mother was with daughters aged 12 and 9 for her attack. He called on people to remain calm.
Streets around the bombed churches were blocked by checkpoints and heavily armed police stood guard as forensic and bomb squad officers combed the area for clues.
Television footage showed one church where the yard in front appeared engulfed in fire, with thick, black smoke billowing up.
All six of the suicide bombers were killed in the attack.
LeBron James Never Stopped Trusting his Teammates
Jonas Valanciunas took advantage of the Cavaliers' willingness to surrender the paint to score 18 points in less than 16 minutes. James had played every other night dating back to Game 5 of the Pacers series.
The attacks come several days after five Indonesian police officers and an inmate were killed in clashes at a high-security jail on the outskirts of Jakarta.
A gun and suicide attack in the capital Jakarta left four attackers and four civilians dead in January 2016, and was the first assault claimed by IS in Southeast Asia.
IS said it was behind the riot, a claim authorities rejected.
Police have only given details of one attack on Santa Maria Catholic Church.
Separately, an internal police report reviewed by Reuters said a suspected bomb exploded in a auto in the parking lot of a Pentacostal church, setting alight dozens of motorbikes.
"They had planned to attack police targets on May 11 but because the police were prepared, they picked alternative targets", National Intelligence Agency spokesman Wawan Purwanto told Metro TV.
Pope Francis offered his prayer to the victims during his Sunday prayer in Rome. Religious minorities in Indonesia, especially Christians, have been repeatedly targeted by militants.
"Together we invoke the God of peace to cease these violent actions, and in the heart of all, find space not for hatred and violence but for reconciliation and fraternity", he said.
Christians, many of whom are from the ethnic Chinese minority, make up about 9 percent of Indonesia's 260 million people.
Jemaah Islamiyah, the network responsible for the Bali attacks, was obliterated by a sustained crackdown on militants by Indonesia's counterterrorism police with US and Australian support.
Elon Musk "super serious" about starting candy company
Moats , a competitive buffer between one's business and the rest of the competition, have historically been used by Warren Buffet. According to CNN , the idea for the candy company stems from a feud between Musk and his fellow billionaire Warren Buffet.
India can qualify for knockout stage, says Constantine
Old rivals and neighbors Iran and Iraq will renew their rivalry when they play each other in their respective first matches. In a pot of powerhouses, the Azkals got the two-time Asian cup champion and 2015 runner-up Korea.
Valeant changing name to distance itself from scandal
WTW holds price to earnings ratio of 40.65 that presents much better indication for a stock's value than the market price alone. MML Investors Services LLC lifted its position in shares of Valeant Pharmaceuticals International by 15.5% in the 4th quarter.