Rescuers pulled 20 children to safety from Harni lake in Vadodara city and are searching for two more who are missing, police and district officials said, adding that some children are undergoing intensive care treatment.
It was not immediately clear how many people were on the boat and local media reports cited overcrowding as a possible reason behind the incident, which police did not confirm.
Senior city police official Anupam Singh Gahlaut said the victims had not been provided life jackets during the boat ride.
He said the children were aged between seven to 13 and studied in a school in Vadodara, which is about 120 kilometres away from Ahmedabad, the largest city of state.
National and local disaster management officers are engaged in the rescue, Gahlaut added.
"Distressed by the loss of lives ... My thoughts are with the bereaved families in this hour of grief," Prime Minister Narendra Modi's office said in a social media post.
Federal government will provide compensation of 200,000 rupees ($2,400) to families of the deceased and 50,000 rupees to the injured, Modi's office said.
The state government also announced compensation of 400,000 rupees for families of the deceased.
