The boy’s 26-year-old mother was luckily saved after her traffic police officer husband pulled her alive from the hole.
The husband had been on duty in the area on Sunday afternoon and used a rope to climb down the hole to safety.
However, the man was unable to rescue his son, who was hurled from his pushchair into the sewer below.
“The woman managed to grab on to the edge of the collapsed pavement, which saved her life,” a Bryansk official was quoted as saying.
Although pieces of the one-and-a-half-year-old boy’s clothing were initially found by found by search teams, it was not until late on Monday afternoon that his body was discovered.
The cause of the pavement collapse is unclear but investigators examining problems with the construction of a local sewage plant.
They have opened a criminal manslaughter case.
Bryansk regional governor Nikolai Denin said a large proportion of the city’s infrastructure was not in the condition it should be.
“We have to start rebuilding things because otherwise this could happen again,” he said.