San Jose police responded to help firefighters with a welfare check at a residential day care around 9:05 a.m., officials said.
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Police say several children fell into a pool.
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Three children were taken to a local hospital in critical condition. Two of the children were pronounced dead. The third child's condition is now considered non-life threatening, police said.
The SJPD Homicide Unit and Santa Clara County District Attorneys Office are investigating the incident.