The driver of the Scania truck, Phillip Potter, 20, his boss Matthew Gordon, 30, and mechanic Peter Wood, 55, face 14 charges in connection with the incident.
Appearing at Bristol Crown Court, they denied all the charges against them.
Mitzi was killed instantly when a "heavily loaded" 30-tonne truck careered down a hill in the Weston area of Bath on February 9 last year, hitting her and her grandmother as they walked down the road.
The trial, expected to last between three and four weeks, is due to open at the court on Tuesday afternoon.
High Court judge Mr Justice Langstaff outlined the case to the prospective jury of seven men and five women.
"On February 9 last year, a lorry, heavily loaded, went down Lansdown Lane in Bath," the judge said.
"In its path along the road, the lorry came into contact with and killed a child - a four-year-old girl - crossing at a pedestrian crossing and injured the grandmother who was taking her across the crossing.
"It hit other cars and there's no dispute that a consequence of those collisions was that three of the occupants of those cars died and others may have sustained injuries.
Potter denied the 10 charges against him, including death by dangerous driving and by careless driving.
The 20-year-old is also charged with causing serious injuries to Karla Brennan and Margaret Rogers - Mitzi's grandmother - by dangerous driving.
Gordon denied the 14 charges against him. He is accused of the manslaughter of Mitzi, Mr Parker, Mr Allen and Mr Vaughan by failing to ensure that the brakes of the truck were in a safe condition.
The 30-year-old is also charged with causing their deaths by dangerous driving and by careless driving, and causing serious injuries to Mrs Brennan and Mrs Rogers by dangerous driving.
Wood is accused of the manslaughter of Mitzi, Mr Parker, Mr Allen and Mr Vaughan by failing to ensure that the brakes of the truck were in a safe condition. He denies all four charges brought against him.
Adam Vaitilingam QC, prosecuting, is expected to open the case at Bristol Crown Court on Tuesday.