Shaunna Broadway's sons, ages five and seven, suffered second and third degree burns while at a water park with their nursery in Oklahoma.
The most horrific image of her eldest son's sunburn (below) has gone viral on social media.
People became aware of the photo after the children's aunt, Amanda Harvey, posted pictures of the boys' burns to the Oklahoma Fox23 Facebook page.
Harvey wrote: "This is my nephew. He and his brother was left outside Friday at Happiness Day Care in Vinita. No sunscreen. They are in so much pain. The eldest is a red head. Please follow up with this!"
The boys' mother said she had dropped her children off at the nursery at 9am, knowing they were going to a waterpark called Splash Pad.
She told BuzzFeed Life: "I got off work at 5pm. and went to pick them up, and they were clearly burned.
"[The employees] were actually making fun of my older son, because both boys got sunburns but he was being a ‘baby’ and crying about it."
She was told the staff didn't have sunscreen and children were told to keep their clothes on her but sons did not.
Broadway said the sun was 118 degrees that day and she even heard on the news people were warned not to go outside.
The mother-of-two was told by the local hospital they couldn't help until the burns blistered, so she used cream and pain medication for her sons.
The next morning, the burns blistered and she said her boys were in "excruciating pain".
Although the hospital lanced the boils and applied cream that day, the mother said they were still in pain so they next day they flew to a children's hospital in Texas.
The mother was told both boys had second-degree burns, but her oldest - the redhead - suffered third-degree burns as well.
On the photo, the mother said the "white stuff" is Silvadene cream.
Officer Bobby Floyd told BuzzFeed Life: "We are investigating the criminal element of neglect with the Oklahoma Department of Human Services.
"We’ve been conducting interviews at the day care, the hospital, and with other parents to see if there’s anything that leads us to conclude it was neglect or child abuse."
Broadway said she is pulling the boys from the daycare centre.