If there is one thing that stands out about the attacks in Indonesia on Sunday and Monday it is that they were carried out by two families — two sets of parents, who together with their own children undertook suicide attacks on four targets.

Key points: Parents co-opting their children in attacks "not a one-off", expert says

Parents co-opting their children in attacks "not a one-off", expert says Indonesia attacks are the first time analysts have seen young children involved

Indonesia attacks are the first time analysts have seen young children involved Attacks likely show "a degree of zealotry" to a particular cause, expert says

The head of the International Centre for Political Violence and Terrorism Research in Singapore, Rohan Gunaratna, said parents co-opting their own children to carry out attacks is a worrying new trend.

"This is not a one-off. We are likely to see more of these attacks," he said.

Just hours after news broke that the people who had bombed three churches were all from the same family, Indonesia's Surabaya province suffered a second attack, also carried out by a couple and their children.

Puji Kuswati, pictured with her children. The family was responsible for the church bombings. ( Supplied )

In the first co-ordinated attacks, 28 people were killed and 57 injured.

The family's father detonated a car bomb at a Pentecostal church, his two sons — aged 17 and 15 — rode explosive-laden motorcycles into a Catholic church, and their mother and two sisters — aged eight and 12 — blew themselves up at an Indonesian Presbyterian Church.

On the following day, a family of five rode two motorbikes into a checkpoint near a police station and detonated explosives, injuring four police officers and six civilians.

An eight-year-old girl, who was wedged between her mother and father during the attack, survived the explosion.

"It's the first time we've seen a family and the first time we've seen young children involved," said Sidney Jones, terrorism expert at the Institute for Policy Analysis of Conflict in Jakarta.

Indonesian authorities have said they suspect that an Islamic State-inspired group Jemaah Ansharut Daulah (JAD) was involved in the attacks.

According to Ms Jones, security officials have said the father of the family that carried out the first attack was an active member of JAD.

It is not clear whether both attacks were carried out by the same group.

"There's a lot more information we need before we can come to that conclusion," she said.

Sorry, this video has expired Witness footage shows a young girl being carried from the Surabaya Police blast site.

Professor Gunaratna agreed that attacks by families are a new phenomenon in the Asia Pacific region, but said that families and couples have tried to use children in bombings in other parts of the world before.

What he thinks is significant about this development is that it shows that terrorists are able to radicalise whole families.

"This requires a family and community-oriented response to fight the threat," he said.

Why would attackers involve their children?

One reason suggested for why attackers chose to involve children is that adults with kids generally arouse less suspicion.

Radical groups initially only recruited men for suicide missions, but then involved women because they were less likely to get stopped.

Now children are being used, because parents with kids are less likely to be checked by security officials.

That explains why extremist groups would be interested in drawing children into deadly attacks but doesn't explain why two parents would willingly involve their own children.

Indonesian police said the parents and their four children were behind the church attacks. ( Supplied )

Damian Kingsbury, Professor of International Politics at Deakin University, said it is common for Islamist jihadists to sacrifice themselves, but they do not usually sacrifice their own family members.

What he thinks might have happened in these instances is that the family, or at least the parents, had a very firm belief that they were going to heaven and wanted to take their children with them.

"This probably shows a degree of zealotry to a particular cause," he said.

Professor Gunaratna also thinks it was ideology that motivated the parents to include their children.

He believes the father would have become radicalised first, and as the head of the family radicalised his wife and his children with extremist propaganda.

Sorry, this video has expired Families martyring their children is 'without precedent'. (Image: AP/Trisnadi)

"Then everyone participates in the attack with the hope they will all enter heaven," he said.

"This is a very dangerous trend."

Professor Kingsbury was also concerned that these are not the last attacks of this nature we will see.

He thinks it is unlikely the families acted alone and were almost certainly associated with a larger group.

"So it's quite possible that there will be further attacks," he said.