The Thane District rural police told PTI that the boy Nikhil S Pathak, had come to the house of his uncle Vijay Shukla at Bhiwandi.
The family went for a picnic to the Sangrila resort and Shukla had asked the boy to be seated near others and not enter the swimming pool.
However, under the pretext of going to the toilet, the boy went to the swimming pool and drowned to death, the police said.