At about 12.30 PM on Tuesday, the girl went to wash her hands after lunch and by mistake she entered the boys' toilet, where the 43-year-old accused was doing cleaning work, said inspector B A Kadam of Khadakpada police station under Kalyan division.
On seeing the girl in the toilet alone, he allegedly molested her and also made obscene gestures at her, Mr Kadam said.
The girl rushed out of the toilet and raised an alarm. She later told her parents about the incident after which a complaint was lodged last night, the police said.
The accused has been booked for assaulting with intent to outrage the modesty of the girl and also under provisions of the Protection of Children from Sexual Offences Act, the police said.