The number of weekly pediatric cases of COVID-19 surpassed 250,000 last week, the highest number of child cases in a week since the pandemic began, according to a new report from the American Academy of Pediatrics and the Children’s Hospital Association. The new numbers come as school-aged children return to the classroom amid spread of the highly contagious delta variant.

The data offer further evidence that the COVID-19 delta variant can spread far more easily in young people than the original strain of the virus.

During the week ending Sept. 2, children represented more than a quarter – or 26.8% -- of newly reported cases, according to the report.

Over the two-week period ranging from Aug. 19 to Sept. 2, researchers also found a 10% increase in the cumulative number of child COVID-19 cases since the beginning of the pandemic (4,593,721 to 5,049,465).

Since the onset of the pandemic, more than 5 million children have tested positive for COVID-19.

And though the percentage of children hospitalized for COVID-19 remains small compared to other age groups, the number of pediatric patients skyrocketed this summer.

According to a report published Friday by the Centers for Disease Control and Prevention, weekly COVID-19–associated hospitalization rates among children and adolescents rose nearly five-fold from late June to mid-August.

Hospitalization rates were also 10 times higher among unvaccinated adolescents ages 12 to 17 than among fully vaccinated adolescents in that same age group, researchers found.

“At this time, it appears that severe illness due to COVID-19 is uncommon among children,” the American Academy of Pediatrics and the Children’s Hospital Association said. “However, there is an urgent need to collect more data on longer-term impacts of the pandemic on children, including ways the virus may harm the long-term physical health of infected children, as well as its emotional and mental health effects.”

The country's rise in COVID-19 cases this summer has been particularly sharp in Republican-led states — particularly in the South, where some governors such as Florida's Ron DeSantis and Texas' Greg Abbott have sought to ban mask mandates in classrooms.

Earlier this week, Miami-Dade County Public Schools reported that 13 of its employees have died of COVID-19 since mid-August – among them, four teachers, seven bus drivers, one security guard and one cafeteria worker.

"These were extraordinary educators and people, and their loss is being felt throughout the community," United Teachers of Dade President Karla Hernandez-Mats told CNN.