The children were headed home for lunch when the truck hit them and a motorcyclist, killing them instantly before it rolled and hit a tractor that was headed in the opposite direction.
According to police, the pupils killed are all girls aged between nine and 12 years.
“We have lost five lives in this incident, four of them are young innocent school children,” Traffic Commandant Samuel Kimaru said of the five who died on the spot.
Drivers of the tractor and truck were rushed to hospital in a serious condition, before one of them succumbed to injuries.
Kimaru said an analysis of the accident showed it most likely occurred as a result of a poorly maintained braking system of the truck that was transporting stones to Webuye town.
Kenya’s road safety record is wanting, with over 3,000 fatalities reported last year.
Transport Cabinet Secretary Michael Kamau has however, vowed to minimise road accidents in the country with strict enforcement of traffic regulations, including the use of alcoblow to check drink-driving.