Alyssa Shepard is in police custody after causing the fatal crash in Rochester.
The children were hit while boarding a bus near 4600 N State Road 25 in Rochester in Fulton County at about 7:15 a.m., police said. Rochester is located about 45 miles south of South Bend.
Police said the children were two 6-year-old twin boys and their 9-year-old sister. An 11-year-old boy was airlifted to a hospital in Fort Wayne Ind.
The 24-year-old driver, Shepard, stayed at the scene and she is cooperating with authorities.
Police said it is unclear why Shepard -- who was driving a 2017 Toyota Tacoma -- didn't stop. The bus had deployed its arm with a stop sign.
ISP is investigating a fatal crash in Fulton County. Preliminary info is three children were struck & killed at a school bus stop near 4600 N State Road 25. @ISPPeru PIO Sgt. Tony Slocum is at the scene. Updated and confirmed info will be sent via news release later today.— Indiana State Police (@IndStatePolice) October 30, 2018
"We all have a responsibility to make sure our children get to and from school safely," Slocum said. "When we're traveling in the early morning hours and early evening hours we've got to anticipate school buses are going to be out. When those stop arms are extended, by law, you are required to stop. This is the exact reason why. We don't want another family to have to go through this."
The school corporation said in a statement, "Our school corporation has suffered a tragedy this morning. We have learned of three student fatalities and one student seriously injured and airlifted to a Fort Wayne hospital as they were hit by a vehicle while boarding their bus.
We have deployed all school counselors to meet the emotional needs of our staff, students and parents.
We are awaiting to learn more confirmed details but wish to ask the community to come together to pray for the families, our students and our staff."
The accident remains under investigation.