The bus and van, which belongs to the Community Worship Center Church of the Nazarene, collided near Brooklyn Avenue and Winthrop Street shortly after 9 a.m., the FDNY said.
The fronts of both vehicles were damaged, the van on its driver's side and the bus on its passenger's side.
At the scene, medical crews evaluated 27 people, 19 of whom were children, a fire spokeswoman said. Everyone refused medical attention at the scene, she added.
Both vehicles remained on the scene. The school bus's passengers continued their journey on another bus, fire said.