The incident took place at around 8 AM when the van carrying school children was hit by Tamsa passenger train going to Varanasi from Azamgarh at Mahaso unmanned crossing in Ranipur area here.
Superintendent of Police AK Shukla said that five children were killed on the spot while eight others were injured in the incident.
The victims are yet to be identified. All of them were students of DD Convent School, Hajipur, police said.
Railway Minister Suresh Prabhu will make a suo motu statement in both Houses of Parliament on the accident.
"Just now, there has been a railway accident. We want to make a statement in Parliament. The Railway Minister has given a notice and I spoke to both the presiding officers. The government wants to take the Opposition in confidence and inform the House," Parliamentary Affairs Minister M Venkaiah Naidu told reporters outside Parliament House.