The 49-year-old Balliang East man was charged with four counts of dangerous driving causing serious injury on Wednesday and will appear in Melbourne Magistrates Court via video link.
Victoria Police Superintendent Michael Cruse said investigators were trying to establish what caused the crash in Melbourne's west on Tuesday.
"Inattention is something that we are actively looking at as part of the investigation," he told reporters.
"We want all road users to remain vigilant, concentrate, obey the speed limits ... and not use their mobile phone."
The bus carrying 45 children had just left Exford Primary School for the day when a truck hit the school bus from behind at Eynesbury, 44km west of the Melbourne city centre, about 3.40pm on Tuesday.
Police say 18 children were taken to the Royal Children's and Sunshine hospitals, with seven seriously injured.
Royal Children's Hospital received nine patients aged five to 11, including two who were discharged after treatment at the emergency department.
Seven patients remain in the Royal Children's, including one in intensive care.
The children have suffered multiple and traumatic injuries ranging from partial and complete amputations, crushed limbs, severe lacerations to head and body, head injuries and glass shard injuries.
Three patients are receiving spinal support.
Two patients are still to go into surgery as of Wednesday afternoon, while four of the more seriously injured will require further surgeries over the coming days and weeks.
The male bus driver sustained minor injuries.
Multiple surgeons were called in for the crisis including the hospital's own doctors, and vascular and specialist microplastic surgeons from Royal Melbourne Hospital.
Several students were trapped inside the bus before witnesses and emergency workers pulled them from the wreckage and took them to hospital.
Exford Primary School principal Lisa Campo said support was being offered to students and parents.
"It's just distressing knowing what our kids have been through and I can only just imagine their fear," Ms Campo told reporters.
"We've got all of the student support services team here today and I've offered that support to the families."
Parents faced an anxious wait overnight before being reunited with their children early on Wednesday morning.Â
Prime Minister Anthony Albanese said the crash was horrific.
"My heart goes out to them and to their families at what must be an extraordinarily difficult time," he said.
Premier Daniel Andrews said he had been in contact with the school.
"The reason I called (the school's principal) last night and again this morning was just to make sure that she knew and understood that 'whatever you ask for ... the answer will be yes. We're there for you'," he said.
Victorian Education Minister Natalie Hutchins said the school would remain open with mental health support workers on the ground.
"Particularly those kids who were involved in the accident but also those children that would have seen the accident last night ... on TV, on social media," she said.
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Kids Helpline 1800 55 1800 (for people aged 5 to 25)
