Hospitals in the US are taking emergency measures to respond to a spike in respiratory viruses among young children.
Some are building overflow tents to house more beds, while others have cancelled planned surgeries.
The US is facing a surge in viruses such as the potentially dangerous respiratory syncytial virus (RSV).
Children under five, especially newborn babies, are most at risk of developing severe symptoms from RSV.
And young children under six months are being taken to hospital with RSV at seven times the rate seen several years ago, according to government data released earlier this month.
Other viruses such as flu, Rhinovirus and coronavirus are also adding to the spike in hospital admissions.
The US Department of Health has said more than three quarters of children's hospital beds were full in November, although experts say this is likely an underestimate.
Hospitals are "bursting at the seams", Daniel Rauch, the chief of Paediatric Hospital Medicine at Tufts Medicine in Massachusetts, told the BBC.
"It's more than we've seen in certainly the last couple of years," he said. "The total volume is more than I've seen in my career - almost three-decades worth."
The Children's Hospital Association, which represents more than 220 hospitals across the country, said several were at "over 100% capacity".
In California, some hospitals are using tents outside of emergency room buildings to make room for additional patients. In Oregon, one children's hospital has had to take emergency steps to allow more space for children in its intensive care unit.
Boston's Children's Hospital in Massachusetts said last month that it would delay elective surgeries due to the surge in respiratory viruses.
Experts believe cases of RSV and flu have surged this year because protective measures like mask-wearing and social distancing during the coronavirus pandemic protected some children from exposure, leaving them more vulnerable to infection this year as people relax those behaviours.
Children's hospitals are still recovering from a reduction in beds due to the coronavirus pandemic, when they made space for adults who are more at risk of severe Covid infections.
The Children's Hospital Association and the American Academy of Pediatrics have asked President Joe Biden to declare a national emergency to help remove some hurdles to expanding paediatric hospital capacity.
RSV is a respiratory illness that typically results in cold-like symptoms for adults, but can be dangerous for young children and those with underlying health conditions as well as older adults.
In severe cases it can cause bronchiolitis, which includes a build-up of inflammation in the lungs and trouble breathing. The US does not have a vaccine for RSV available to all children, although scientists are trying to develop one.