– A wave of deadly bombings Sunday and Monday and evidence of more planned have shaken Indonesia just before the holy month of Ramadan, with entire families — including children — carrying out suicide attacks against Christian worshipers and the police.

The discovery Monday of completed bombs in a housing complex outside Surabaya, Indonesia's second-largest city, came a day after members of a single family carried out three attacks against separate churches in the city around the time of services, killing seven people.

On Sunday night, three members of another family, including a child, were killed when a bomb exploded at their apartment outside Surabaya when the police moved in to arrest them.

And on Monday morning, a family of five riding on two motorbikes detonated a bomb at the entrance of the Surabaya police headquarters — killing all but one of them and injuring four police officers. An 8-year-old girl who was with the attackers survived the blast and was hospitalized.

The extent of the carnage and the fact that children were enlisted in the attacks drew condemnation from the country's leader, President Joko Widodo, who called them "barbaric." All told, 12 civilians and 13 terrorist suspects were dead from two days of violence, with at least 46 people injured, including police officers.

Police officials said the attackers, whether by blood or other ties, were working together.

"They're from one organization," Gen. Tito Karnavian, chief of the National Police, said during a Monday news conference in Surabaya. The city, the capital of East Java Province with a population of almost 3 million, has a large ethnic Chinese Christian community.

A day earlier, Karnavian had said the family suspected in those attacks had recently returned to Indonesia after being deported from Syria.

On Monday, Karnavian said the bombs that exploded Sunday and Monday were similar in their construction — highly powerful and sensitive to movement — to those used by ISIS in its war in Iraq and Syria.

ISIS has claimed responsibility, describing each of the bombings as a "martyrdom" operation carried out by three modes of attack: a car bomb, a suicide vest and a motorcycle-borne bomb.

Indonesia, the world's most populous Muslim-majority nation, practices one of the most moderate forms of Islam in the world, but still has a homegrown terrorism problem.

The use of children in terrorist plots, analysts say, represents a new and shocking development in Indonesia. "It was in one way expected and also completely unexpected, and that raises it to a new level of sick, using kids in this kind of thing," said Ken Conboy, a counterterrorism analyst in Jakarta.