The incident took place late last evening, when an employee, who had come provide water to the undertrials, opened the door of the observation home.
The juveniles pulled him inside and locked him inside the barrack, the police said.
After that they went towards the main gate and attacked the security guard with rods.
They snatched the keys to main gate from him and fled, leaving the injured guard behind.
The other employees of the observation home raised an alarm and informed the police.
Police officials said that efforts are on to nab the escapees.