Police officials said the accident took place at state highway near Mohanpur village in the district.
An SUV, which was travelling at a high speed, rammed into a sugarcane laden truck parked on the roadside, police said.
"The deceased have been identified as Abhishek Kumar (12), Rajani Kumari (14) and Bablu Paswan (26).
"The SUV passengers had alighted from Amprapali Express at Begusarai Railway Station and were going to Sikarhula village to meet a relative who was ill," said Mufassil Station House Officer (SHO) Rajesh Ranjan.
The bodies have been sent for post mortem examination.