Ashley Malinga was targeted at lunchtime on Monday as he walked home from pre-school.
The Chronicle newspaper reported that the three boys – a seven-year-old and two eight-year-olds – are believed to have forced the tot to strip before beating him around the head.
Ashley’s grandfather only found his body by the side of the road on Monday evening.
The attack has horrified many Zimbabweans, leading to calls for the authorities to ensure children are picked up from pre-school by a responsible adult and not left to walk miles home alone.
Ashley and the boys who attacked him were neighbours in the Nyamandlovu farming area in western Zimbabwe. They played together regularly, relatives said.
One of the boys found out on Monday that Ashley had “beaten up” his sister at pre-school the previous week. The boy’s sister and Ashley are understood to have been in the same class at pre-school, which is known as Grade Zero in Zimbabwe. There is no suggestion she had been seriously hurt.
Police in rural Matabeleland North province have confirmed receiving a report of the attack.
The mother of one of the boys said she was “at a loss for words” over what her son and his friends are alleged to have done, the Chronicle reported.
Police inspector Siphiwe Makonese said: “We’ve received the report of the murder but can’t say much at the moment as investigations are still under way.”
A post-mortem examination will be carried out in Bulawayo, Zimbabwe’s second city.
The boys have not been named because of their age. But a partially-obscured photograph of the three of them, arms draped around each other, was published by state media.
The boys have been “innocently playing and running around” since Monday and do not appear to understand what they have done, one of their mothers told the Chronicle.
Ashley’s grandfather Saul Ncube said: “I’m really shocked by the boys’ behaviour because they were close to my grandson and played together on a daily basis. We’re all neighbours. I’m deeply saddened … The boys ordered [him] to undress and then assaulted him with sticks until he passed out while his cousin helpless watched.”
Ashley lay dead undiscovered for several hours, apparently because of a garbled account of events from the cousin, who is also in pre-school and saw the attack, the child told his grandfather Ashley had “fallen asleep” on the way home.
Mr Ncube did not set out to find Ashley immediately. His delay in reacting has earned him criticism from locals. But in many farming areas in Zimbabwe, schoolchildren often walk back home from school in groups without any adults accompanying them. Few incidents are reported. Streams of children wearing bright uniforms are a common sight along many rural roads here. Tiny preschoolers are often among them. Depending on how far away the school is, the trek can take hours.
When night fell and there was still no sign of the preschooler, Ashley’s grandfather set out to find him.
“We found him naked and lying dead by the roadside. He was bleeding from the head where he had sustained two deep cuts. The boy showed signs that he had been dead for some hours,” Mr Ncube told the Chronicle.
Though some local officials are blaming “evil spirits”, the attack has also reignited the debate on parenting skills and discipline in schools in Zimbabwe after the courts banned corporal punishment earlier this year.