Indiana State Police said the crash occurred just before 10 p.m. Thursday on I-65 near Roselawn, about 30 miles south of Gary.
Sgt. Tony Slocum said an SUV driven by Yvette Williams, 35, of Atlanta, Ga., was rear-ended by a northbound semitrailer while Williams was stopped in a work zone. The impact pushed the SUV into a semi in front of it and ignited a fire that engulfed the SUV and damaged both semitrailers.
The semitrailer was driven by Howard Stratton, 55, of Grand Rapids. He was taken to a hospital complaining of pain.
The other semi driver wasn't injured.
The SUV was so badly damaged that emergency crews weren't able to confirm the number of victims until mid-day Friday, Slocum said.
Police identified the dead as Williams, Jamin Osborne, 5, and Jasmin Osborne, 7, all of Atlanta; and Amado Mangual, 49, Lindsey Williams, 27, Yazmin Goldman, 5, and Arielle Goldman, 3, all of Merrillville.
Slocum said neither alcohol nor narcotics was believed to be a factor in the crash.
Police said the crash is still being investigated and that final results will be sent to the Jasper County prosecutor's office for review.