At least seven children died when a small wooden boat carrying 10 people overturned Saturday at a lake near Sao Paulo, authorities said.

The children — believed to be between the ages of 5 and 11 — drowned when their boat took on water and capsized at the Billings Lake in the outskirts of Sao Paulo, according to the Sao Paulo State Civil Defense Department.

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Two more children and one adult were injured, authorities said. Their condition were not immediately known.

Police still were investigating the cause of boat wreck but said the craft may have been overloaded.

The children's parents were barbecuing by the lake and had rented the boat to take the kids for rides, authorities said.