More than 121,000 new COVID-19 cases were reported among kids last week, another "substantial" increase from weeks prior, the American Academy of Pediatrics and the Children’s Hospital Association said in a report.

Last week, children represented 18% of all reported cases. Children represented 15% of cases the week prior.

Pediatric COVID-19-related hospital admissions have now equaled the most seen at any point of the pandemic.

Severe illness due to COVID-19 remains "uncommon" among children, the two organizations wrote in the report. In states which reported virus-related deaths by age, 0.00%-0.03% of all child COVID-19 cases resulted in death.

However, AAP and CHA warned that there is an urgent need to collect more data on long-term impacts on kids "including ways the virus may harm the long-term physical health of infected children, as well as its emotional and mental health effects."

-ABC News' Arielle Mitropoulos

Over the weekend, the daily case average in the U.S. rose to 120,000 -- skyrocketing 930% since mid-June, federal data showed.

Every state in the country is now reporting high or substantial community transmission, according to federal data.

The country's daily death average has increased to nearly 550 per day, a 155% jump in the last month.

The rate of hospital admissions among people under 49 years old is now at its highest point of the pandemic, according to federal data.

-ABC News' Arielle Mitropoulos

Before Los Angeles students could enter their classrooms on the first day of school Monday, many waited in lines so staff could ensure they completed their daily pass health screening.

Los Angeles Unified School District students and staff had to be tested for COVID-19 by the first day of school, Los Angeles Mayor Eric Garcetti said last week. As the year gets underway, students will wear masks and undergo weekly testing regardless of vaccination status, ABC Los Angeles station KABC reported.

All school district employees are required to be fully vaccinated by Oct. 15.

Pfizer/BioNTech have submitted early booster shot data to the Food and Drug Administration.

Phase 1 data found that people given a third shot eight to nine months after their primary doses had a boosted immune response and higher neutralizing antibody levels against the delta variant.

Pfizer/BioNTech plan to continue to study booster shots and submit additional data to the FDA.

It's not clear when or if the FDA and Centers for Disease Control and Prevention might recommend booster doses for all. Only severely immunocompromised people are currently eligible.

-ABC News' Sony Salzman

As COVID-19 cases surge pediatricians are experiencing a first: sick children facing both respiratory syncytial virus, or RSV, and COVID-19.

"We've not seen this before -- we have two very highly contagious respiratory viruses circulating at the same time, particularly throughout the South around Texas and neighboring states," Dr. Jim Versalovic, pathologist-in-chief at Texas Children's Hospital, told ABC News Live on Monday.

Infants, young children and older adults are most at-risk for RSV, a respiratory virus that's usually more prevalent in the fall and winter. RSV kills 100 to 500 children under 5 each year, according to the Centers for Disease Control and Prevention.

"It's not surprising now to see children being impacted with both viruses, particularly infants and young children who are most susceptible to respiratory syncytial virus," Versalovic said.

He said in "recent weeks we've had 30% or more of our pediatric ICU beds [filled] with RSV infections," including some children also with COVID-19, which "could "mean more severe respiratory illness."

"We do know how to treat these children with RSV and with COVID. And so, for now we're managing that, but it is certainly a new challenge for us," Versalovic said.