(NEXSTAR) – Health officials in one Texas city are trying to figure out how two children under the age of 12 received adult doses of the COVID-19 vaccine. Dorothy White, the City of Garland’s public & media relations director, confirmed to Nexstar that the children were both given an injection of the Pfizer vaccine on Sunday, Oct. 31. – two days before the Centers for Disease Control and Prevention approved shots for children ages 5 to 11.

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The parents of one of the children, who is 6, told KTVT that a nurse at a pop-up clinic run by the health department assured them that their child was eligible to receive it.

“They asked us our kids ages, and so we told them 4 and 6, and they said ‘the 6-year-old can obviously get it if you’d like to go ahead and do that,’” Julian Gonzalez recalled. “Going off their confidence and what we read [on the form] we were all for it.”

Gonzalez said his child and a 7-year-old neighbor boy both got shots at the clinic, located at a Baptist church. On Monday, health officials reached out the families to inform them of the mistake.

According to the CDC, children ages 5 to 11 are supposed to receive a dose one third the size of an adult’s. The needle used to administer the vaccine to children in that age group is smaller and specially designed.

White said in a statement that Garland health officials “are in communication with the parents of the children involved, who are monitoring the children for side effects.” She added that the health department reported the incident to the state and continues to investigate the circumstances leading up to “the error.”

“We’re just on edge completely until we see this through,” Gonzalez said. Apart from some initial side effects Gonzalez said his son is doing well. The mother of the 7-year-old told KTVT that her son hasn’t suffered any ill effects from getting the triple dose.

The CDC is urging parents to vaccinate their kids against COVID-19 after clinical trials found the Pfizer vaccine safe for that age group. Officials found the risk of serious illness or death among children from COVID-19 to be greater than the rare adverse reactions from the vaccine.