More kids are being hospitalized with COVID. Experts say we need to vaccinate more people, and use masks in schools.

• There's been a slight rise in children being hospitalized with COVID in several US states.
• Doctors are worried more kids could develop life-threatening complications in the weeks ahead.
• More vaccinated adults, and more masks for the unvaccinated, would both help.

As the Delta variant spreads its far more infectious version of COVID-19 across the country, a very small wave of new childhood cases is beginning to raise alarm bells among doctors, particularly in lesser vaccinated areas of the US.

The shift is noticeable at Intermountain Primary Children's Hospital in Utah, where there were barely any children hospitalized with COVID-19 in May and June. Last week, a handful of kids were hospitalized with the coronavirus, and three were receiving treatment there as of Tuesday evening.

In Mississippi, it's a similar story: there are seven kids in the hospital, two of them on ventilators. It's a troubling statistic for Dr. Thomas Dobbs from the Mississippi State Department of Health, who tweeted: "please be safe."

According to the Centers for Disease Control and Prevention's official tally, 490 children under the age of 18 have died from COVID-19 in the US so far during the pandemic, 164 of them babies and toddlers under the age of four.

Without an authorized vaccine available to youngsters under 12 years old yet, young children (along with unvaccinated teens and adults) are now at greatest risk of developing a life-threatening case of COVID-19, and the rare but potentially fatal multisystem inflammatory syndrome (MIS-C) associated with it.

For now, kids under 12 "depend on the adults and adolescents to get vaccinated in order to slow or halt transmission," Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine, told CNN .

Until we reach a high rate of vaccination nationally, doctors say, kids cannot drop masks, especially as they flock back to school.

Kids with COVID-19 can develop a rare inflammatory syndrome, or long COVID

"In any other time, if we had a new disease that killed 300 children, we would be pulling out all the stops, we would be doing everything we could to protect them," Dr. Andrew Pavia, the chief of pediatric infectious diseases at the University of Utah told Insider.

"And yet people are saying, 'well, it's not so bad, because it's nothing like what happens to adults.'"

The most dangerous time for kids who get COVID-19 is not when they're suffering through the disease, Pavia says.

It typically takes three to six weeks after that for children to develop MIS-C, a rare condition that can impact both mild and severe COVID-19 cases.

Even if children don't get MIS-C, there are still long-term risks. Hotez told CNN that as many as 30% of children infected with COVID-19 will have long COVID.

Doctors worry about kids going maskless at school this fall

Utah had great success with safe in-person schooling last year, by adopting a layered approach to disease prevention.

"We know how to actually have kids come back to the classroom and do it safely: ventilation, a reasonable amount of spacing, and strict mask use," Pavia said.

Nationally, masks they also nearly eliminated another deadly childhood illness. There was only one reported flu-related pediatric death in the entire US.

But new political moves in Pavia's state now make it near-impossible for schools to mandate masks.

"I'm very worried," he added.

Dr. Megan Ranney, an emergency-medicine physician at Brown University, wrote on Twitter Wednesday: "Saying that kids can be affected by Covid does not mean schools need to stay closed. "Conversely, saying that schools should be open does not mean that masks and vaccines aren't needed."

New mask-relaxing guidance from the CDC is being taken as a license to shun masks at school too. But the reality is, disease experts still agree everyone who's unvaccinated (over the age of two) should wear their mask in the classroom, and that's what the CDC still suggests.

"The best way to make in-person schooling safe is for all unvaccinated people to wear masks all the time in the classroom, as part of a layered strategy," Pavia said.

Vaccinating more middle- and high-schoolers, as well as teachers, parents, and staff, is also critical.

"They deserve protection just as much as older people," Pavia said of children under 12, who are not yet eligible for vaccination.