Two of the occupants -- the mother of the child and a flight assistant -- were severely hurt in the accident, which occurred as the 45-year-old pilot was attempting to land the helicopter in a parking lot on a military-owned field in the canton of Glaris.
The rear of the aircraft touched the ground on approach, unbalancing it, the police said.
The helicopter was operated by a firm that transports both passengers and cargo.
The ATS news agency said the pilot and two flight assistants had gone to pick up a couple and their child in the region. The couple were doing forestry work.