East Lampeter police announced Monday that the Lancaster County district attorney’s office, Pennsylvania Department of Agriculture and the U.S. Food and Drug Administration are joining the investigation of children drinking a caustic substance Friday at a local restaurant.

Related: East Lampeter police investigate if incident was criminal or accidental

Ten-year-old Richie Zaragoza and his 4-year-old half-sister Ginaya Mercado are in fair condition after they each drank the substance in their apple juice during a birthday meal at Star Buffet & Grill.

Both children were rushed to the hospital and spent Saturday night in intensive care at Hershey Medical Center with severe burns of the mouth and throat.

They are being treated for the effects of what is still an undetermined substance that made its way into the children's juice during Richie’s birthday celebration at the restaurant, located at 2232 Lincoln Highway East, near the Tanger Outlets.

Soon after Ginaya drank the juice and began vomiting, Richie started throwing up blood and screaming, “It burns, it burns,” his mother, Virginia Davis, said Saturday.

Related: 'It burns, it burns': Children rushed to hospital after drinking caustic substance

A spokeswoman for the medical center said Monday morning that both children are in "fair condition."

Richard Zaragoza Sr., Richie’s father, told LNP Sunday morning that the burns were confined to his son’s throat area and did not negatively affect his stomach.

Richie, who also has cystic fibrosis and diabetes, is still sedated with an intubation device, which could be removed as early as Monday, Zaragoza said. Doctors were also looking into the cause of blood in the boy’s urine this morning, he said.

Davis, Ginaya’s mother, did not immediately return a phone call Sunday morning. But Zaragoza said family members have relayed to him that Ginaya is doing better and no longer sedated.

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He said Richie has been mostly sedated but has tried to communicate in quick moments of waking up.

“I had to try to talk to him last night through his fingers,” Zaragoza said. “I told him I loved him … and he squeezed my hand twice so he was responsive.”

Doctors say he will not be able to eat food for a week, Zaragoza said.

Police said the two children had severe reactions after drinking apple juice from foam cups.

Another child, 6, experienced stomach discomfort, and an adult male had burns in his mouth after tasting the juice, police said. They were treated at Lancaster General Hospital and released. No other patrons reported reactions or discomfort, police said.

Zaragoza told LNP tests are still underway, but he said a test from the Hershey Medical Center revealed that methanol was at least one of the substances present in the juice.

Methanol, according to the Centers for Disease Control and Prevention, is a “toxic alcohol that is used industrially as a solvent, pesticide, and alternative fuel source.” It is also found in fresh fruits and vegetables, fruit juices, fermented beverages and diet soft drinks with aspartame.

“Most methanol poisonings occur as a result of drinking beverages contaminated with methanol or from drinking methanol-containing products,” according the CDC.

Steve Weng, manager of Star Buffet & Grill, said Sunday he’s never seen anything like this and does not know how it happened. The juice, he said, came from a local supermarket.

Weng said he has not been able to call the family, but he said he would like to tell them nobody wanted this to happen.

Calls to East Lampeter Township police Monday have not been returned.