SURABAYA, Indonesia — Famela, 8, excelled at math and martial arts. Her sister, Fadhila, 12, was good at drawing. Firman, 15, was on the student council at the liberal Muslim experimental school they attended, and he had a soft spot for Taylor Swift. Yusuf, 17, liked to make videos and take care of his little sisters.

All four children were seen as being astonishingly well-behaved and accomplished by their neighbors and friends in their multiethnic residential enclave in Surabaya, Indonesia’s second-largest city. They all wondered how the parents, Dita Oepriarto and Puji Kuswati, did it.

But by Sunday morning they wondered if they had really known the family at all, after back-to-back bombings at three Christian churches. Famela, Fadhila, Firman and Yusuf blew themselves up in the attacks, as did their parents, killing 12 bystanders and wounding at least 40 others.

To the end, the children were dutiful. Mr. Oepriarto set off a bomb in their family Toyota at the Surabaya Center Pentecostal Church. Around the same time, the teenage boys rode together on a motorcycle to the Roman Catholic Santa Maria Church, where they set off their explosives. The father massacred seven people; his boys killed five others.