(CNN) Mexican health officials are investigating after two babies died and 29 children were hospitalized from suspected adverse reactions to shots from the country's national vaccination program.

Six of the children hospitalized in the southern Mexican state of Chiapas remain in serious condition, the Mexican Social Security Institute said on Sunday

The parents of the two infants who died were so outraged at the government that they refused to let authorities perform autopsies, CNNMexico reported

The illnesses were reported after 52 children from the rural mining community of La Pimienta were given vaccines Friday for tuberculosis, rotavirus and Hepatitis B, the institute said. Later that night, 31 of the children "presented adverse reactions presumably associated with the application of these vaccines," officials said. Two of the children later died.

Authorities haven't said what they think caused the illnesses. They've pinpointed the batches the vaccines came from and have suspended administration of other vaccines from those batches pending the conclusion of their investigation, the institute said . They're also investigating the needles used in the vaccinations and the possibility that a virus or bacteria could have caused the illnesses, Mexico's El Universal newspaper reported

Residents of La Pimienta told CNNMexico the vaccinations were offered Friday when officials came to the community and announced over loudspeakers that vaccines would be given to newborns.

In the poor, rural area, access to medical care is difficult to come by. There are no hospitals or clinics, only a small cinder block health center with a tin roof where residents go when a doctor passes through the community. A small selection of paracetamol and other pills sits on dusty shelves inside.

On Sunday officials said the state's governor and the director general of the Mexican Social Security Institute visited the hospitalized children, vowing to support their families and to be transparent as they continued their investigation.