A California girl died while undergoing a simple dental procedure on Monday, leaving her parents with unanswered questions in her death, her family said.

Daleyza Avila Hernandez, 3, was getting two teeth pulled and caps put on two others at the Children's Dental Surgery Center in Stockton, east of San Francisco, her family told Fox 40.

"My daughter was very healthy," Araceli Avila said. "All I did was I take my daughter to the dentist because they were going to fix her teeth, and about 30 minutes later they brought her back dead."

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Avila and her husband, Jose Hernandez, recalled seeing the toddler "vivacious and full of life" just before the procedure. The parents said they weren't allowed into the surgery room. But while waiting, Avila saw an ambulance pull up to the office.

"And I stood up and went outside because I was like, 'they are coming for a kid,' but I never thought it was for my child," Avila said.

A nurse told them their daughter's heart stopped, possibly from underlying heart issues. Daleyza Avila Hernandez was taken to the hospital and pronounced dead.

David Thompson, the administrator of Children's Dental Surgery Center in Stockton, told Fox 40 that Hernandez had a reaction to the anesthetics during the procedure. She was stabilized before being transported to the hospital, though Thompson said he didn't know what caused her death. He added the girl's parents weren't allowed in the room due to sanitary rules.

Thompson said staff members at the center were well trained and have years of experience.

"We’re committed to helping kids every single day. That’s our mission, that’s why we’re here. It’s risky. Not everyone wants to do it," he told Fox 40.

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However, the Hernandez family said they still don't understand what led to their daughter's death.

The Dental Board of California said in a statement to Fox News:

"The Dental Board of California is aware of the tragic situation. An investigation is underway so specific details of the case cannot be shared at this time. Consumer protection is the board’s highest concern and we want to extend our deepest sympathy to the family."

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