A man has died a week after allegedly being assaulted outside a primary school just moments after students were picked up at the end of the day.

Police say the 63-year-old man was assaulted at a reserve near Strathaird Primary School in Narre Warren South about 3.15pm on June 12.

He was rushed to hospital with critical injuries but died on Thursday.

A Department of Education spokesperson told AAP on Friday they were aware of a distressing incident that occurred near the school last week.

"Our immediate focus is on supporting the school community," the spokesperson said.

"The safety and wellbeing of students and staff is always our priority.

"Those who witnessed the incident have been offered wellbeing support and the school is working closely with families."

Two men, a 21-year-old man of no fixed place of address and a 22-year-old Narre Warren South man were charged last week with recklessly causing serious injury.

They remain in custody.

Homicide Squad detectives are now taking lead of the investigation, with further charges possible.

Police believe the parties involved were known to each other.