HERMOSILLO, Mexico (AP) – Grieving parents buried their children Sunday after a devastating day care fire killed 40 infants and toddlers, stunning Mexico and prompting its president to promise a thorough investigation.

Funeral processions drove slowly to churches in the north-western city of Hermosillo decorated with balloons and flowers.

The family of two-year-old Maria Magdalena Millan dropped white roses on her casket and attached a Dora the Explorer balloon to the cross marking her grave at one of the first funerals held on Saturday.

“I love you and I don’t want to leave you here!” her mother screamed.

President Felipe Calderon arrived in the city late Saturday. He wished surviving children a speedy recovery and promised families full government support and a thorough investigation into the fire’s cause.

“I want to say to the mothers and fathers of the little ones who died that we share their profound sadness,” Calderon said earlier in the day.

The death toll rose to 40 on Sunday after two children died in hospitals, according to Sonora state health secretary Raymundo Lopez Vucovich. Most of the victims had died of organ failure caused by smoke inhalation, he said.

The fire initially spread from an adjoining tire and car warehouse to the roof of the ABC day care and sent flames raining down. Fire officials still don’t know how it started.

Delfina Ruelas, 60, said her grandchild German Leon died of his burns on Saturday, three days after his fourth birthday.

She and her husband saw televised reports about the fire Friday and rushed over.

“I thought he wasn’t that burned and that we would find him OK, but he was very burned,” said Ruelas, dissolving into tears outside the morgue, where she waited with 30 other relatives. “They operated on him yesterday, and he held on, but today he couldn’t.”

Firefighters carried injured children out the day care’s front door – its only working exit – and through large holes that a civilian knocked into the walls before rescue crews arrived, according to a fire department official who spoke on condition of anonymity because he was not authorised to speak publicly about the fire.

Francisco Lopez, who works at nearby auto repair shop, said he rushed to the scene in his pickup truck and rammed it in reverse three times against the wall of the day care to break a hole in it.

The deaths in Hermosillo, capital of the state of Sonora, again raised questions about building safety in Mexico. Officials cracked down on code violations last year after a deadly stampede at a nightclub killed 12 and a disco fire nine years ago killed 21. Both clubs were in Mexico City.

An estimated 142 children, ranging from six months to five years in age, were in the day care at the time of the fire, along with six staffers who looked after them, Sonora state Governor Eduardo Bours told a news conference.